Introduction• Brain & s.c. comprise the CNS• Brain is protected by cranium & meninges –
• Consists of 3 layers:1. dura mater2.
3. pia mater
Meninges
1. Dura mater –
2. Arachnoid mater – thin &
weblike; no b.v. or nerves
SUBARACHNOID SPACE –
3. Pia mater – delicate; w/b.v. & nerves; attached
directly to brain & follows contours
Importance of Meninges
• dural sinus – spaceformed when d.m.splits into 2 layers
• subdural hematoma –fluid & blood collectsunder d.m. from trauma
• Meningitis –
Partitions of Dura mater
1. Falx cerebelli –
2. Falx cerebri – b/t rt. & lt.cerebral hemispheres
3. Tentorium cerebelli – b/tcerebrum & cerebellum
The Spinal Cord
• Consists of 31 segments• Each gives rise to a spinal
nerve• Provides 2-way communi-
cation b/t brain & body• 2 main functions:
1. 2.
The Spinal Cord
• Beginning pt. – foramenmagnum
• Ending pt. – conus medullaris (narrow pt. b/t L1-L2)
• Cauda equina –
Cross Section – Spinal Cord
• Gray matter –
• White matter –
• 2 grooves divide s.c.into rt. & lt. halves:posterior median sulcusanterior median fissure
Nerve Tracts
• White matter in s.c.consists of fibers callednerve tracts; provide 2-waycommunication b/t brain & s.c.;
• 2 types:1. ascending –
*In the medulla, fibers cross over
Reflexes • S.C.- center for reflexes
(automatic, subconscious responses)
• Reflexes control many involuntary actions (HR, resp.rate, swallowing, sneezing, etc.)
• - reflex arc.
• One of the simplest – patellar reflex (helps maintain an upright position)
• Involves only 2 neurons, sensory& motor (no interneuron)
Parts of a Reflex Arc
• Most reflexes include 5 structures:1. receptor2. 3. interneuron4. motor neuron5.
• Other examples:withdrawal reflex (occurswhen a person touches something painful) plantar reflex, Babinski reflex (abnormal in adults), biceps, triceps & ankle jerk reflexes
Ventricles of Brain
• Ventricles - Interconnected cavities in brain -
4 ventricles:1st (left hemisphere)2nd (rt. hemisphere)3rd (midline of brain)4th (in brainstem)
Pathway of CSF Circulation
1. Most CSF produced in lat. ventr. by choroid plexuses
2. Interventricular foramina –openings; allow CSF toflow from lat. to 3rd ventr.
3. 3rd ventricle4. Cerebral aqueduct –
5. 5. 4th ventricle
CSF Circulation6. Flows into central canal & SA space of s.c. & back to subarachnoid space of brain7.
8. Drain into blood-filleddural sinus into circ. sys.
Humans secrete approx. 500mlof CSF daily.Only about 150 ml in CNS at anygiven time (continuously reabsorbed)CSF -
Lumbar Puncture
• Needle inserted intosubarachnoid spaceof s.c. & CSF is withdrawn
• Site is usually b/t L1-L2 or
L3-L4 (a.k.a. spinal tap)• A manometer used to
measure CSF pressure• CSF can be analyzed for
viruses, bacteria, bleeding,tumors of the n.s., MS, & early-onset Alzheimers
Normal vs. Hydrocephalic Brain
←Normal
Normal Brain Hydrocephaly Normal intracranial Excessive accumulation pressure 7-15 mm Hg of CSF causes ventricles in brain to dilate; infant’s skull expands & incr. in circumference (bulging
fontanels possible)
Treatment of Hydrocephaly
• Shunt placed in brain to regulate pressure & reabsorb CSF into subarachnoid space
Cerebrum
• Largest part of brain• Consists of 2 halves (hemi-
spheres)•
• Convolutions – • Sulci – • Fissures – 2 deep grooves
1. Longitudinal – divides brain into rt. & left halves
Cerebrum
2. Transverse –separates cere-brum from cere-bellum
• Cerebral cortex –
• White matter – under gray;makes up most of the cerebrum
Functions of Cerebrum
• 3 basic functions:1. Motor area – sends
impulses to muscles2. Sensory area – interpret
impulses from sensory receptors
3. Association area –
Lobes of the Brain
• Sulci divide each cerebral hemisphere into 5 functional areas called lobes (named for skull bones).
• 5th lobe - insula
(not shown)
Lobes of the Brain
1. Frontal• Association areas –
• Motor areas –(ant. to central sulcus) –control of voluntary muscles• Broca’s area – ant. to motor cortex & in left hemi.; coordinates muscles of speech
Lobes of the Brain
2. Parietal – • Somato-
sensory area – cutaneous & other senses
• Associationarea –
Lobes of the Brain
3. Occipital – visual area
4. Temporal –
• Wernicke’s area – inleft temporal lobe; controlsanalysis of spoken language
5. Insula –
Basal Ganglia
• Also called basal nuclei
• Consist of gray matter deep within the cere-bral hemispheres
•
• Produce the ntm dopamine that inhibits motor functions (decr. levels assoc. w/Parkinson’s disease)
Diencephalon
• Includes 2 regions:1. Thalamus – receives
all sensory info &channels it to correctregion on cerebralcortex for interpret-ation
2. Hypothalamus –
Pineal & Pituitary Glands
• Also located in diencephalon
• Pineal gland –
• Controls sleep &wake cycles
• Pituitary gland –
Midbrain
• 1st, short sectionof brainstem
• Relays info. fromlower parts of b.s.& s.c. to higher brain
• Contains corporaquadrigemina –
Medulla Oblongata
• Enlarged contin-uation of s.c.
• All nerve tracts pass thru here &many cross over
•
Medulla
• Contains 3 centers:1. Cardiac center – area
that controls heart rate2. Vasomotor center –
3. Respiratory center –
• Nonvital centers – coughing, sneezing, swallowing, vomiting also located in medulla
Reticular Formation
• Nerve fibers scattered throughout the b.s.
• When sensory impulsesreach the r.f., it respondsby activating the cerebralcortex into wakefulness
•
• If the r.f. is destroyed, a personremains in a comatose state
Reticular Formation
• The r.f. filters incoming sensory info& decides what is important
• Decreased activity in the r.f. results in sleep
• Types of Sleep:1. Slow-wave (non-REM)-
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