Physiology of CNS

Dr. Awni KhraisAssociate Professor

Faculty of Pharmacy, Philadelphia UniversityEmail: a_khrais@philadelphia.edu.jo

At the end of this chapter, students will be able to:

1. Describe the components of a reflex arc.

2. Name the types of sensory receptors found in the skin.

3. Discuss the relationship of sensory receptors to touch, cold,

warmth, and pain.

4. Describe the muscle spindles and their role in the stretch reflex.

5. Describe the ascending and descending tracts of spinal cord and

their main functions.

6. Describe the basal ganglia and list the pathways that interconnect

them, along with the neurotransmitters in each pathway.

7. List the pathways to and from the cerebellum and the connections

of each within the cerebellum.

8. Describe the function of hypothalamus, thalamus, sensory and

motor cerebral cortex.

Learning Outcomes

Organization of nerves system

• A- CNS1: BRAIN

2: SPINAL CORD

• B- PERIPHERAL NERVOUS SYSTEM.

Organization of the Brain

• Composed of gray and white matter

• Different organization than in the spinal cord

– Centrally located gray matter surrounded by white matter

– Cortex: external sheets of gray matter in cerebrum & cerebellum (some parts of brain)

– Nuclei: deep masses of gray matter surrounded by white matter

(some parts of brain)

The Brain

• 4 Parts– Cerebrum– *Diencephalon– Brain Stem

• Midbrain• Pons• Medulla

– Cerebellum

• Gray matter surrounded by White matter w/outer cortex of gray matter

*some texts consider this part of brain stem

Cerebrum

• “Executive Suite” of nervous system

– Self-awareness, initiate + control voluntary movements, communicate, remember, understanding, language

• Most superior region

• Covers diencephalon + top of brain stem like mushroom cap

• Cerebral cortex

Cerebral Hemispheres

• Fissures and Grooves

– Fissures – deepest• Transverse cerebral fissure

– Separates cerebral hemispheres from cerebellum

• Longitudinal fissure

• Separates R and L cerebral hemispheres

– Sulci• Grooves on surface

– Gyri • Ridges of brain tissue among the sulci

Cerebral Hemispheres:

• Each hemisphere divided into 5 lobes– Frontal

– Parietal

– Occipital

– Temporal

– Insula

• Created by deep sulci

• Functional areas: motor, sensory

• Associative areas: integrate

Cerebral Hemispheres

• The 2 hemispheres control opposite sides of body

• Corpus callosum– The largest commissure between the hemispheres

• Hemispheres specialized for different cognitive functions– Left Cerebral hemisphere

• Language, mathematics and logic

– Right Cerebral hemisphere• Visual-spatial, interpreting facial expressions, intuition,

emotion, artistic/musical skills

Diencephalon

• Surrounded by cerebral hemispheres• Made of 3 Paired Structures

– Thalamus “gateway”• Communicates sensory info of cerebral cortex

– Hypothalamus• Regulates many body activities• Emotion, sleep, memory, etc.• Pituitary Gland

– Growth Hormone– Thyroid Stimulating Hormone

– Epitheliums• Pineal Gland

– Melatonin

Brainstem

• Midbrain, Pons, Medulla Oblongata

– Passage of all signals between spinal cord and brain

– Regulates basic physiological functions

– Innervation of head and neck

Brainstem

• Midbrain

– Visual and Auditory reflex centers

– Attachment for CN III, IV

• Pons

– Attachment for CN V, VI, VII, VIII

• Medulla oblongata

– Regulates several basic physiological functions

– Attachment of CN IX, X, XI, XII

Cranial Nerves

• 12 Pairs: I-XII

• Numbered Anterior to Posterior

• Attach to inferior surface of brain

• Exit brain through foramina in skull

• I + II attach to Forebrain (cerebrum + diencephalon)

• III-XII attach to Brainstem (midbrain, pons, medulla)

• Only X goes beyond the head-neck

• I Olfactory

• II Optic

• III Oculomotor

• IV Trochlear

• V Trigeminal (1-3)

• VI Abducens

• VII Facial

• VIII Vestibulocochlear

• IX Glossopharyngeal

• X Vagus

• XI Accessory

• XII Hypoglossal

Cranial Nerve Function

• I Olfactory--------Sensory--smell

• II Optic-------------Sensory--vision

• III Oculomotor----Motor----extrinsic eye muscles

• IV Trochlear-------Motor----extrinsic eye muscles

• V Trigeminal

• V1 Opthalmic-----Sensory-cornea, nasal mucosa, face skin

• V2 Maxillary------Sensory-skin of face, oral cavity, teeth

• V3 Mandibular---Motor-muscles of mastication

• ---Sensory-face skin, teeth, tongue (general)

Cranial Nerves (continued)

• VI Abducens--------------Motor-----eye abduction muscles

• VII Facial-------------------Sensory---part of tongue (taste)

• -------------------Motor------muscles of facial expression

• VIII Vestibulocochlear---Sensory----hearing, equilibrium

• IX Glossopharyngeal----Motor------stylopharyngeus muscle

• ----Sensory----tongue (gen & taste), pharynx

• X Vagus------------------Motor-------pharynx, larynx

• -------------------Sensory----pharynx, larynx, abd. organs

• XI Accessory-------------Motor------trapezius, sternocleidomastoid

• XII Hypoglossal----------Motor-------tongue muscles

Summary of Functional Groups

• Purely Sensory = I, II, VIII

• Primarily Motor = III, IV, VI, XI, XII

• Mixed = V, VII, IX, X

• Parasympathetic Fibers = III, VII, IX, X(Division of Autonomic NS = Visceral

Motor)

Parasympathetic Fibers

• CN III = Oculomotor– Contracts Iris (controls pupil)– Contracts Ciliary Muscle (controls lens)

• CN VII = Facial – Innervates Salivary glands (mandibular & sublingual)– Innervates Lacrimal gland

• CN IX = Glossopharyngeal– Innervates Parotid Salivary gland

• CN X = Vagus– Innervates thoracic & abdominal viscera

Cerebellum

• Smooths + coordinates body movements directed by other parts of brain

• 2 Cerebellar Hemispheres

• Cerebellar cortex surrounds Arbor vitae

• Functions

– Information on equilibrium

– Movement of neck, trunk, limbs

– Information from cerebral cortex on voluntary movement

BRAIN MENINGES

Meninges: 3 membranes around brain and spinal cord

• Made of Connective tissue

• Functions

– Cover, Protect CNS

– Enclose, protect blood vessels supplying CNS

– Contain CSF

• 3 Layers

– Dura Mater (external)

– Arachnoid Mater (middle)

– Pia Mater (internal)

Meninges (continued)

• Dura mater

– Strongest, 2 Layers, Fibrous Connective Tissue

• Periosteal layer (Periosteum): External/superficial layer

• Meningeal layer: Internal/deep layer

– Layers fused except around Dural sinuses (venous blood filled internal jugular vein)

Extensions of Dura Mater

– Partitions: limit movement of brain

• Flax Cerebri –vertical, between cerebral hemispheres

• Flax Cerebelli -vertical, between cerebellar hemispheres

• Tentorium Cerebelli –horizontal, between cerebrum and cerebellum

Meninges

• Arachnoid Mater

– Middle layer

– Subarachnoid Space-between arachnoid mater and pia mater (contains most of CSF, blood vessels)

– Arachnoid Villi (Granulations)- projections of arachnoid mater through dura into superior sagittal sinus, act as valves to help CSF pass into dural sinuses

Meninges (continued)

• Pia Mater

– Innermost layer

– Delicate, highly vascular

– Clings directly to brain tissue, dips into convolutions

• The bone of the skull is covered by hair, Athick layer immediately below the skull is called DURA MATTER,

• The brain tissues ( cerebral cortex) is covered by PIA MATTER.

• Between the Pia Matter and the Dura Matter there is another layer which is called Arachnoid Mater. (Spider).

• The space between archnoid and pia mater is called subarachnoid space which is filled with

cerebrospinal fluid (CSF)

• The brain is suspended by CSF fluid which is flow down to spinal cord as well

Ventricles

• Expansions of brain’s central cavity

• Lined with Ependymal Cells

• Filled with CSF (cerebrospinal fluid)

• Ventricles continuous w/each other + central canal of spinal cord

Ventricles (continued)

• Lateral Ventricles (#1+2)– Cerebral Hemisphere– Separated by Septum Pellucidum

• Third Ventricle– Diencephalon– Interventricular Foramen: connects to lateral ventricle

• Fourth Ventricle– Hindbrain– Cerebral Aqueduct: connects 3rd and 4th ventricles– Connects to central canal of spinal cord & medulla– 3 openings connect 4th to subarachnoid space

• 2 lateral apertures• 1 median aperture

Cerebrospinal Fluid

• Liquid cushion for brain and spinal cord

• Nourishes brain

• Removes waste

• Conducts chemical signals between parts of CNS (e.g. hormones)

• Forms as a filtrate of blood in choroid plexuses

Choroid Plexuses

• Choroid Plexuses: groups of capillaries surrounded by ependymal cells

• Made of sodium, chloride ions, proteins, glucose, O2

Flow of CSF

• Formed in Choroid plexuses

• Through Ventricles

• Into Subarachnoid space & central canal from 4th ventricle

• Through Arachnoid Villi into Superior Sagittal Sinus

• Into Internal Jugular Vein

Blood Brain Barrier

• Protects brain from blood-borne toxins (e.g. urea, food toxins, bacteria)

• Endothelium of brain capillaries are loaded with tight junction to decrease permeability

• Not complete protection, some things still have to get through (e.g. fat-soluble molecules can pass through)

Blood Supply to Brain

• Arteries – External carotid arteries and branches

• Tissues of head & face, skin, muscles• Middle meningeal a. = brain

– Boxers!

– Internal carotid arteries and branches• Ophthalmic a. = Eye & Orbits• Ant & Middle Cerebral arts = Cerebrum• Branches form Cerebral Arterial Circle = Anastomosis

– Vertebral arteries• Posterior brain• Vertebrae & Cervical Spinal Cord• Branches form Cerebral Arterial Circle = Anastomosis

Blood Supply to the Brain

• Veins– Dural sinuses

• Superior & Inferior Sagittal, transverse, sigmoid, straight, etc

– Internal jugular

• Receives from dural sinuses

– External jugular

• Drains scalp and face (superficial)

– Vertebral

• Drains cervical vertebrae, cervical spinal cord, small neck muscles

Spinal nerves

THE REFLEX ARC

COMPONENTS OF REFLEX ARC

Motor vs. Sensory Nerves

• Sensory = Afferent

– Send nervous impulse from sensory receptors to brain to bring in information

– e.g. pressure, temperature, pain

• Motor = Efferent

– Send nervous impulses from brain to body to accomplish an action

– e.g. movement of a muscle, activation of a gland

Motor Nerves

• Motor Nerves

– Visceral Motor (motor innervation muscle in viscera + glands)

• innervation smooth + cardiac muscle, glands

– Somatic Motor (motor innervation of skeletal muscle)

• innervation of skeletal muscles (except pharyngeal arch m.)

Sensory Nerves

• Sensory = Afferent

– Visceral Sensory (sensory innervation of viscera)

• stretch, pain, temp., chemical changes, irritation in viscera

• Special: taste

– Somatic Sensory (sensory innervation of outer part body)

• touch, pain, pressure, vibration, temp. in skin, body wall, limbs

• Special: hearing, equilibrium, vision, smell

MOTOR NEURON

MOTOR NERVE

• Nerves and a muscles are excitable cells, they transmit electrical activities.

• Dendrites (trees like) they are short branches, they transmit electrical impulses to the nerve cell body.

• The cells body are gray matter and they are attached to the nerve axon.

• The first part of axon, as small elevation known as axon helix.

• The motor nerve is surrounded by insulating cells called Schwann cell, they produce fatty material known as myelin. In the CNS oligodendrocytes cells produce myelin substance, if there is a damage to these cells the patient will suffer from demyelinating disease, (e.g. : multiple sclerosis)

• The Schwann cells are interrupted by a nurofiber node( Node of Ranvier).

• The action potential started at the axon helix and travel across the motor nerve from node to node, this type of transmit ion is called :

Saltatory propagation of action potential.

• At the end of axon there is a motor end bulb, attached to the muscle fiber at the neuromuscular junction.

• At the presynaptic membrane the acetylcholine vesicles rupture and Ach neurotransmitter will be released from these vesicles and go to synaptic cleft and bind with Ach receptors at postsynaptic terminal by which action potential occur and produce depolarization of these receptors, to produce contraction of the muscle.

• This called Excitation- contraction coupling.

The Sensory nerve V Motor nerve

Reflex Arc• The reflex arc governs the operation of reflexes. Nerve

impulses follow nerve pathways as they travel through the nervous system. The simplest of these pathways, which include only a few neurons, is called the reflex arc. Reflexes whose arc passes through the spinal cord are called spinal reflexes.

Parts of the Reflex Arc

1. Receptor – detects the stimulus. a) Description: the receptor end of a particular dendrite or a specialized receptor cell in a sensory organ. b) Function: sensitive to a specific type of internal or external change.

2. Sensory neuron – conveys the sensory info. to brain or spinal cord. a. Description: Dendrite, cell body, and axon of a sensory neuron. b. Function: transmit nerve impulses from the receptor into the brain or spinal cord.

Parts of the Reflex Arc

3. Interneuron: relay neurons. a. Description: dendrite, cell body, and axon of a neuron within the brain or spinal cord. b. Function: serves as processing center, conducts nerve impulses from the sensory neuron to a motor neuron.

4. Motor neuron: conduct motor output to the periphery. a. Description: Dendrite, cell body, and axon of a motor neuron. b. Function: transmits nerve impulse from the brain or spinal cord out to an effecter.

Parts of the Reflex Arc

5. Effector: a. Description: a muscle or gland. b. Function: Response to stimulation by the motor neuron and produces the reflex or behavioral action.

Spinal Reflexes

The Myotatic Reflex•Stretch reflex: Muscle pulled tendency to pull back•Feedback loop•Discharge rate of sensory axons: Related to muscle length•Monosynaptic•Example: knee-jerk reflex

Spinal Reflexes

Reverse myotatic reflex•Regulate muscle tension•Golgi tendon organs

Spinal Reflexes

Reciprocal inhibitionContraction of one muscle set accompanied by relaxation of antagonist muscle

Flexor reflex: Complex reflex arc used to withdraw limb from aversive stimulus

Crossed-extensor reflex:Activation of extensor muscles and inhibition of flexors on opposite side

Stretch and Deep Tendon Reflexes

For skeletal muscles to perform normally:

The Golgi tendon organs (proprioceptors) must constantly inform the brain as to the state of of the muscle.

Stretch reflexes initiated by muscle spindles must maintain healthy muscle tone.

Muscle Spindles

• Are composed of a few intrafusal muscle fibers that lack actin and myosin in their central regions, are noncontractile, and serve as receptive surfaces.

• Muscle spindles are wrapped with two types of afferent endings: primary sensory endings of type Iafibers and secondary sensory endings of type II fibers and secondary sensory endings of type II fibers.

• These regions are innervated by gamma ( ) efferent fibers.

• Note: contractile muscle fibers are extrafusal fibers and are innervated by alpha ( ) efferent fibers.

Stretch Reflex

Stretch Reflex

• Stretching the muscle activates the muscle spindle.

• Excited motor neurons of the spindle cause the stretched muscle to contract.

• Afferent impulses from the spindle result in inhibition of the antagonist inhibition of the antagonist.

• Example: patellar reflex.

Tapping the patellar tendon stretches the quadriceps and starts the reflex action.

The quadriceps contract and the antagonistic hamstrings relax.

Golgi Tendon Reflex

• The opposite of the stretch reflex.

• Contracting the muscle activates the Golgi tendon organs.

• Afferent Golgi tendon neurons are stimulated, neurons inhibit the contracting muscle, and the antagonistic muscle is activated.

• As a result, the contracting muscle relaxes and the antagonist muscle contracts.

Golgi Tendon Reflex

• The terminals of the spindle sensory fibers make direct excitatory synaptic contact with alpha motor neurons serving the ordinary muscle fiber (extrafusal fibers).

• Contraction of these fibers shorten the muscle and relaxes the spindle fibers terminating the stretch reflex and muscle contraction.

Events in the Monosynaptic Stretch Reflex -Summary

• 1. Passive stretch of a muscle (produced by tapping its tendon) stretches the spindle (intrafusal) fibers.

• 2. Stretching of a spindle distorts its central (chain) region, which stimulates dendritic endings of sensory nerves.

• 3. Action potentials are conducted by afferent (sensory) fibers into the spinal cord on the dorsal roots of spinal nerves.

• 4. Axons of sensory neurons synapse with dendrites and cell bodies of somatic motor neurons located in the ventral horn gray matter of the spinal cord.

• 5. Efferent impulses in the axons of somatic motor neurons (which form the ventral roots of the spinal nerves) are conducted to the ordinary (extrafusal) muscle fibers. These neurons are (alpha) motor neurons.

Events in the Monosynaptic Stretch Reflex -Summary

• 6. Release of Ach from the endings of alpha motor neuron stimulates the contraction of extrafusal fibers, and thus the whole muscle.

• 7. Contraction of the muscle relieves the stretch of its spindles, thus decreasing electrical activity in the afferent nerve fibers, and relaxes the spindle fiber and terminates the stretch reflex and muscle contraction. the stretch reflex and muscle contraction.

• Note: By sending command to the motor neurons, the brain set a muscle’s length. The stretch reflex makes sure the muscle stay at that length. The stretch reflex is therefore important for maintaining muscle tone and upright posture.

The Deep Tendon Reflex

- If you tap on the tendon of a muscle, it contracts. Its synergists contract and its antagonists are inhibited. -polysynaptic reflex.

- A tap on the patellar tendon stretches the extensor muscle and its spindles.

• The spindle discharges and excites the associated sensory fibers that excite the motor neurons to the extensor muscle.

• - Contraction of the extensor muscle extends the lower leg (knee -jerk).

• - Ipsilateral flexor muscle relax for extensors to function.• - Branches of the sensory fibers from muscle spindle activate

inhibitory interneuron, which in turn, inhibit the motor neuron to the flexor muscle.

The Withdrawal Reflex (Flexor Reflex)

• The automatic withdrawal of an extremity from a painful stimulus.

• A polysynaptic reflex.

• Sensory pain signals excite motor neurons to the flexor muscles, eliciting flexion and withdrawal of the leg.

• Motor neurons to the extensor muscles are inhibited via inhibitory interneurons.

• This would relax the extensors of the same leg.

The Withdrawal Reflex

The Crossed Extensor Reflex

• A polysynaptic reflex.

• E.g., Painful stimulation of one foot causes flexion (withdrawal) of the ipsilateral leg as well as the extension of the contralateral leg, to stabilize the posture; thus the ipsilateral leg flexors are activated and the extensors are inhibited and vice versa in the contralateralleg.

Clinical Terms

• Analgesia: loss or reduction in the ability to sense pain, without loss of consciousness.

• Analgesic: pain – relieving drug. • Anesthesia: loss of feeling. • Ataxia: partial or complete inability to coordinate

voluntary movements. • Epilepsy: Disorders of the CNS that is characterized by

temporary disturbances in normal brain impulses; it may be accompanied by convulsive seizures and loss of consciousness.

• Huntington disease: Hereditary disorders of the brain producing progressively worsening, uncontrollable dance-like movements and personality changes.

• Neuralgia: sharp, recurring pain associated with a nerve, usually caused by inflammation or injury.

Clinical Terms

• Analgesia: loss or reduction in the ability to sense pain, without loss of consciousness.

• Analgesic: pain – relieving drug. • Anesthesia: loss of feeling. • Ataxia: partial or complete inability to coordinate

voluntary movements. • Epilepsy: Disorders of the CNS that is characterized by

temporary disturbances in normal brain impulses; it may be accompanied by convulsive seizures and loss of consciousness.

• Huntington disease: Hereditary disorders of the brain producing progressively worsening, uncontrollable dance-like movements and personality changes.

• Neuralgia: sharp, recurring pain associated with a nerve, usually caused by inflammation or injury.

Cerebral cortex

• All the neurons are interneurons– By definition confined to the CNS

– They have to synapse somewhere before the info passes to the peripheral nerves

• Three kinds of functional areas– Motor areas: movement

– Sensory areas: perception

– Association areas: integrate diverse information to enable purposeful action

Sensory areasPosterior to central sulcus

• Primary somatosensory cortex: postcentral gyrus of parietal lobe (allows

conscious awareness of sensation and the ability to localize it: wherethe sensation is from)

• Somatosensory association area: behind it (understanding of what is being felt:

the meaning of it)

From special sense organs• Sight: occipital lobe

– Primary visual cortex (17)• Handles info from

contralateral retina (right ½ of visual field is on left side)

• Map of visual space• If damaged: functionally blind

because no conscious awareness of sight

– Visual association area (18 & 19)• Face recognition is usually on

the right side

• Hearing: temporal lobe– Primary auditory area (41)– Auditory association area

(22)

Refer back to this labeled version as needed

Motor areas Anterior to central sulcus

• Primary motor area

– Precentral gyrus of frontal lobe (4)

– Conscious or voluntary movement of skeletal muscles

• Primary motor area continued

– Precentral gyrus of frontal lobe

– Precise, conscious or voluntary movement of skeletal muscles

– Large neurons called pyramidal cells

– Their axons: form massive pyramidal or corticospinal tracts

• Decend through brain stem and spinal cord

• Cross to contralateral (the other) side in brainstem

• Therefore: right side of the brain controls the left side of the body, and the left side of the brain controls the right side of the body

Motor areas – continued• Broca’s area (44): specialized motor speech area

– Base of precentral gyrus just above lateral sulcus in only one hemisphere, usually left

– Word articulation: the movements necessary for speech

– Damage: can understand but can’t speak; or if can still speak, words are right but difficult to understand

Motor areas – continued

• Premotor cortex (6): complex movements asociated with highly processed sensory info; also planning of movements

• Frontal eye fields (inferior 8): voluntary movements of eyes

Homunculus – “little man”• Body map: human body spatially represented

– Where on cortex; upside down

Association Areas

• Tie together different kinds of sensory input

• Associate new input with memories

• Is to be renamed “higher-order processing“ areas

Prefrontal cortex: cognition

Executive functioninge.g. multiple step problem solving

requiring temporary storage of info (working memory)

This area is remodeled during adolescence until the age of 25 and is very important for well-being; it coordinates the brain/body and inter-personal world as a whole

Social skillsAppreciating humorConscienceMoodMental flexibilityEmpathy

IntellectAbstract ideasJudgmentPersonalityImpulse controlPersistenceComplex ReasoningLong-term planning

Wernicke’s area

– Junction of parietal and temporal lobes

– One hemisphere only, usually left

– (Outlined by dashes)

– Pathology: comprehension impaired for written and spoken language: output fluent and voluminous

but incoherent

(words understandable

but don’t make sense;

as opposed to the

opposite with Broca’s

area)

Region involved in recognizing and understanding spoken words

Cerebral white matter• Extensive communication

– Areas of cortex with each other

– Areas of cortex with brain stem and spinal cord

• Via (mostly) myelinated axon fibers bundled into tracts– Commissures

– Association fibers

– Projection fibers

• Commissures: interconnect right and left hemispheres so can act as a whole– Corpus callosum is largest

• Association fibers: connect different parts of the same hemisphere; can be long or short

• Projection fibers: run vertically

– Cerebral cortex running down (with motor instructions)

– Or ascend to cerebral cortex from below (sensory info to cortex)

• Corona radiata: spray of projection fibers

– From precentral (motor) gyrus

– Combines with sensory fibers traveling to sensory cortex

– Form a band of fibers called internal capsule*

___________Sensory input to brainMotor output from brain__________

*

• Projection fibers – Corona radiata:

fanning out of the fibers

– Internal capsule: bundled, pass down

• Commisure– Corpus callosum:

connects right and left hemispheres

• Decussation: crossing of pyramidal tracts

_________________

___________________

________________

_____________________

Ascending and Descending tracts

• Ascending tracts

These tracts are bundles of neurons transmitted information from the sensory nerves of the spinal cord to cerebral cortex,

Descending tracts

These tracts send motor information via motor nerves to the targets (Effectors organ; locomotor system, glands and blood vessels).

White matter of the spinal cord

• Ascending pathways: sensory information by multi-neuron chains from body up to more rostral regions of CNS– Dorsal column– Spinothalamic tracts– Spinocerebellar tracts

• Descending pathways: motor instructions from brain to more caudal regions of the CNS– Pyramidal (corticospinal) most important to know– All others (“extrapyramidal”)

• Commissural fibers: crossing from one side of cord to the other• Most pathways cross (or decussate) at some point• Most synapse two or three times along the way, e.g. in brain

stem, thalamus or other

Major fiber tracts in white matter of spinal cord

Damage: to motor areas – paralysisto sensory areas - paresthesias

sensory motor

Ascending tracts

• 1: Dorsal column TractThese are only ascending and they are

transmitted the information of

DSCRIMINATION.

VIBRATION.

PROPRIOCEPTION

They are modern sensation.

Dorsal spinothalamic tract

• This tract started from fasculus cuneuatus and fasculus Gracillus and pass to brain stem to medulla oblongata, from M.O the Rt Gracillus Nx and Rt cuneuatus Nx cross to the opposite side and second ordered neuron travel to thalamus.

Posterior or dorsal spinothalamic tract

– Receptor↓ .( Vibration, Discrimination, Proprioceptor),

– sensory neuron↓

– The neuron pass ipsilaterally to medulla oblongata.↓

– From M.O Rt cuneuatus and Rt Gracillus cross to the opposite side via Medial lemniscus. ↓.

– Third order neuron pass to somatosensory cortex,

2: lateral and Anterior Spinothalamic tracts

• These tract started from the dorsal sensory root ↓

• Then cross to the contralateral side↓.

• A second order neuron pass to thalamus ↓.

• From the thalamus a third order neuron pass to sensory cortex.

The lateral spinothalamic tract

• Transmits pain and temperature sensation.

• The Anterior spinothalamic tract,

transmitted crude touch and pressure.

Note:

Fasculus : nerve cells comes in circle,

Lemniscus: cells body come in flat.

Dorsal tract v lateral and Anterior tracts .

Only ascending Ascending and Descending

Highly myelinated Moderately myelinated

Highly localized Less/poorly localized.

Fast conducting Slow conducting.

Highly developed Primitive developed

Concerned with:ProprioceptionBody positionVibrationDiscrimination2 points discriminationFine touch.

Concerned with:Crude touchTemperaturePainPressure.

Major ascending pathways for the somatic senses

Spinocerebellar: proprioception from skeletal muscles to cerebellum of same side (don’t cross)

Dorsal column: discriminative touch sensation through thalamus to somatosensory cortex (cross in medulla)

Spinothalamic: carries nondiscriminate sensations (pain, temp, pressure) through the thalamus to the primary somatosensory cortex (cross in spinal cord before ascending)

(thousands of nerve fibers in each)

Descending tracts of CNS

Corticospinal tract

1: lateral corticospinal tract

80 % of its fibers decussate just below M.O.

2: The anterior corticospinal tract .

20% of its fibers not decussate.

Corticospinal tract pathways

• This motor tract started in the motor cerebral cortex. → Internal capsules→ Mid Brain, Pons, M.O (nerves fibers decussate at medulla oblongata). → THEN they travel to spinal cord

At the anterior horn → motor nerve will activate the skeletal muscles.

Some DescendingPathways

Pyramidal tracts: Lateral corticospinal – cross in pyramids of medulla; voluntary motor to limb muscles Ventral (anterior) corticospinal – cross at spinal cord; voluntary to axial muscles

“Extrapyramidal” tracts: one example

Synapse with ventral (anterior) horn interneurons

UPER MOTOR NEURON V LOWER MOTOR NEURON

UPER MOTOR NEURON WITH MOTOR FIBERS COME FROM THE MOTOR CORTEX UNTIL THE ANTERIOR HON CELL. THE LOWER MOTOR NERONS STARTED FROM THE ANTERIOR HORN CELLS TO THE SKELETAL MUSCLES ( UMN: Before synapse LMN: After

synapse).

UMN LESION LMN LESION

SPASTIC FLACCID

HYPERTONIC HYPOTONIC

HYPERREFLEXIA

HYPOREFLEXIA

DISUSED ATROPHY

DEENERVATI-ON ATROPHY

+ BABINISKI - BABINISKI

EXTRAPYRIMIDAL TRACTS

TRACTS DESCENDING FROM CEREBRAL CORTEX BUT NOT

CROSSING AT THE M.O.

1: VESTIBULOSPINAL TRACTACTIVATES EXTENSOR AND INHIBITS

MUSCLES2: OLIVOSPINAL TRACT3: - RUBROSPINAL TRACT

- RETICULOSPINAL TRACTACTIVATES FLEXOR AND

INHIBITS EXTENSOR4:TECTOSPINAL

POSTURE REFLEX RELATED TO VISION VIA SUPERIOR COLLICULUS.

Basal ganglia• Subcortical motor nuclei

• Part of “extrapyramidal system”

• Cooperate with cerebral cortex in controlling movements

• Most important ones: caudate nucleus, lentiform nucleuscomposed of putamen and globus pallidus

• Not part of basal forebrain nuclei (which are related to arousal, learning , memory and motor control)

Transverse section

• Internal capsule passes between diencephalon and basal ganglia to give them a striped appearance

– Caudate and lentiform sometimes called corpus striatum because of this

Basal ganglia• Subcortical motor nuclei

• Part of “extrapyramidal system”

• Cooperate with cerebral cortex in controlling movements

• Most important ones: caudate nucleus, lentiform nucleuscomposed of putamen and globus pallidus

• Not part of basal forebrain nuclei (which are related to arousal, learning , memory and motor control)

Transverse section

• Internal capsule passes between diencephalon and basal ganglia to give them a striped appearance

– Caudate and lentiform sometimes called corpus striatum because of this

Basal ganglia• Cooperate with cerebral cortex in controlling

movements• Communicate with cerebral cortex, receive input

from cortical areas, send most of output back to motor cortex through thalamus

• Involved with stopping/starting & intensity of movements

• “Dyskinesias” – “bad movements”– Parkinson’s disease: loss of inhibition from substantia nigra

of midbrain – everything slows down– Huntington disease: overstimulation (“choreoathetosis”) –

degeneration of corpus striatum which inhibits; eventual degeneration of cerebral cortex (AD; genetic test available)

– Extrapyramidal drug side effects: “tardive dyskinesia”• Can be irreversible; haloperidol, thorazine and similar drugs

Basal ganglia

• Note relationship of basal ganglia to thalamus and ventricles

Transverse section again

Diencephalon (part of forebrain)Contains dozens of nuclei of gray matter

• Thalamus

• Hypothalamus

• Epithalamus (mainly pineal)

Thalamus (egg shaped; means inner room)– Two large lobes of gray matter (over a dozen nuclei)– Laterally enclose the 3rd ventricle– Gateway to cerebral cortex: every part of brain that

communicates with cerebral cortex relays signals through a nucleus in the thalamus (e.g. certain nucleus for info from retina, another from ears, etc.)

– Processing (editing) occurs also in thalamus

Coronal section

HypothalamusForms inferolateral walls of 3rd ventricle

Many named nuclei

Coronal section

Hypothalamus• “Below thalamus”

• Main visceral control center– Autonomic nervous system (peripheral motor neurons

controlling smooth and cardiac muscle and gland secretions): heart rate, blood pressure, gastrointestinal tract, sweat and salivary glands, etc.

– Emotional responses (pleasure, rage, sex drive, fear)

– Body temp, hunger, thirst sensations

– Some behaviors

– Regulation of sleep-wake centers: circadian rhythm (receives info on light/dark cycles from optic nerve)

– Control of endocrine system through pituitary gland

– Involved, with other sites, in formation of memory

Hypothalamus

(one example of its functioning)

Control of endocrine system through pituitary gland

Epithalamus• Third and most dorsal part of diencephalon

• Part of roof of 3rd ventricle

• Pineal gland or body (unpaired): produces melatonin signaling

nighttime sleep

• Also a tiny group of nucleiCoronal section

Cerebellum Two major hemispheres: three lobes eachAnteriorPosteriorFloculonodular

Vermis: midline lobe connecting hemispheres

Outer cortex of grayInner branching white matter, called “arbor vitae”

Separated from brain stem by 4th ventricle

Functions of cerebellum

• Smooths, coordinates & fine tunes bodily movements• Helps maintain body posture• Helps maintain equilibrium• How?

– Gets info from cerebrum re: movements being planned– Gets info from inner ear re: equilibrium– Gets info from proprioceptors (sensory receptors informing where the

parts of the body actually are)– Using feedback, adjustments are made

• Also some role in cognition

• Damage: ataxia, incoordination, wide-based gait, overshooting, proprioception problems

Functional brain systems(as opposed to anatomical ones)

Networks of distant neurons that function together

Limbic system

Reticular formation

Limbic system (not a discrete structure - includes many brain areas)

• Most important parts:– Hipocampus– Amygdala– Cingulate gyrus– Orbitofrontal cortex (not labeled; is behind eyes - part of

the prefrontal cortex but connects closely)

Limbic system continued

• Called the “emotional” brain• Is essential for flexible, stable, adaptive functioning• Links different areas so integration can occur

– Integration: separate things are brought together as a whole– Processes emotions and allocates attentional resources

• Necessary for emotional balance, adaptation to environmental demands (including fearful situations, etc.), for creating meaningful connections with others (e.g. ability to interpret facial expressions and respond appropriately), and more…

Reticular formation

Runs through central core of medulla, pons and midbrain

• Reticular activating

system (RAS):

keeps the cerebral

cortex alert and

conscious

• Some motor control

REFERENCES: PHYSIOLOGY

Required Physiology II textbook: Hall, J.E., Guyton and Hall Textbook of Medical Physiology, 12th ed., 2011, Elsevier/SaundersISBN 978-1-4160-4574-8.

Supplementary Physiology II TEXTBOOKS:

1. Koeppen B.M., Stanton B. A. Berne and Levy Principles of Physiology, 6th ed. 2010, Elsevier / Mosby ISBN: 978-0-323-07362-22. Boron, W.F., Medical Physiology - A Cellular and Molecular Approach, 2ed, Elsevier 2010. ISBN 978-1-4160-3115-4.3. Ganong, W. F., Review of Medical Physiology, 23nd ed., 2010 McGraw-Hill Book Company, ISBN 978-0-07-1605678-0.4. Rhodes and Bell, Medical Physiology: Principles for Clinical Medicine,

3rd ed. 2009, Lippincott Williams & Wilkins.

Print copy: ISBN 978-0-7817-6852-8

E-Book: ISBN 9781609139339

5. Johnson, L.R., Essential Medical Physiology, 3rd. ed., 2003 Academic PressISBN 987-0-12-387584-6.6. Purves, D., et al, Neuroscience. 4th ed., Sunderland, MA, Sinauer Associates, Inc. 2008.ISBN: 978-0-87893-697-77. Silverthorn, D., Human Physiology: An Integrated Approach, 5th ed. 2010, Prentice HallISBN 987-0-321-555980-7

MONOGRAPHS1. West, J.B., Respiratory Physiology, 8th ed., 2008, Lippincott Williams& Wilkins.ISBN:978-0-7817-7206-82. Levitzky, M., J.B., Pulmonary Physiology, 7th

ed., 2007, McGraw-Hill Book Company.ISBN: 978-0-07-143775-23. Koeppen and Stanton, Renal Physiology, 4th ed., 2007, Elsevier, Mosby.ISBN:978-0-323-03447-0MONOGRAPHS (continued)4. Eaton, and Pooler, Vander’s Renal Physiology, 7th ed., 2009, McGraw-Hill Companies

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