More on the nervous system

Central nervous systemspinal cordbrain

Cranial and spinal nerves

Autonomic nervous system

Nerve pathways

afferent nerves (sensory) INTO CNSvia dorsal (posterior)root of peripheral nerve

efferent (motor) FROM CNS via ventralroot of peripheral nerve (anterior)

may be simple arc, or move longtudinallyor transversely within gray matter of spine

A reflex arc

Brain and spine are protected by skeleton

Meninges formed between skeleton and tissue,provide additional protection

Subarachnoid space filled with cerebrospinalfluid (CSF)formed by choroid plexusalso fills ventricles in brain

Cerebrospinal fluid protects the central nervous system

Organization of spinal cord

31 pairs of spinal nervesinnervate specific parts of body

Tracts from muscles to brain, and back again

Corticospinal (pyramidal)- movementExtrapyramidal- balance and posture

Spinothalamic- “generalized” sensoryinformation

Ascending (sensory) and descending (motor)

Brain

Cerebrum- sensory, motor, higher order function

Midbrain, diencephalon, etc- processing sensoryinformation, other integrative function

Cerebellum- coordinating voluntary movement

Pons- respiratory regulation

Medulla oblongata- various visceral organs(heart, lungs)

Cerebrum

Left and right hemispheres

Separated by falx cerebri

Connected by corpus callosum

Functional regionssensorymotorassociation

Crossover in brain stem: right hemispherecontrols movement of left side, etc.

Corpus callosum allows communicationbetween hemispheres

Most people have a dominanthemisphere

Basal nuclei• Direct and modify

motor response• Parkinson’s disease:

lack of dopamine- movement is inhibited (region becomes OVERactive

• Huntingdon’s disease: basal nuclei degrade

Diencephalon- a small area of the brain, buta lot is happening!

Thalamus- filters and directs sensory informationPituitary gland- many hormonesHypothalamus-homeostasis

Limbic system- hypothalamus, thalamus, basalnuclei, hippocampus, amygdala

“Survival instincts”, emotions, memory(fear, anger, aggression, sex drive)

Regions of the brain

Brain stemmidbrain- reflex centers nerve tracts

pons- tracts, regulation of breathing rateand depth

medulla oblongata- cardiac, respiratory,digestive, vasomotor (blood supply)

Reticular formation- wakefulness (RAS)

Cerebellum- coordination

Drugs and the nervous system (see p. 245)

Depressants affect neurotransmitter secretion

Barbituates act throughout brain, especiallyon RAS

Benzodiazepines (“tranquilizers”) depresslimbic system and RAS

Opiates- stimulate opioid receptors, relieve pain

Cannabinoids- release inhibitions, depresshigher brain centers

Stimulants vary in mechanisms

Cocaine- affects serotonin and dopamine levels

Amphetamine- adrenalin (epinephrine) levels

Caffeine- systemic

Nicotine- affects serotonin, dopamine andhormone secretion

Why are they addictive?

How does the brain communicate with the rest of

the body?• Peripheral nervous system

– Cranial– Spinal

• Sensory• motor