Structure of Nervous System

Nervous system

Communication network and control centre of the body, consists of brain, spinal cord and nerves

Divisions of nervous system

Central and peripheral, afferent and efferent, autonomic and somatic, sympathetic and parasympathetic

Comparison of somatic and autonomic divisions

Effectors - autonomic acts on heart muscle, involuntary muscle, glands. Somatic acts on skeletal muscles

General function - autonomic: homeostasis, somatic: response to external environment

Efferent pathways - autonomic: 2 nerve fibres from the CNS to the effector with a synpase in a ganglion, somatic: one nerve fibre from CNS to effector

Neurotransmsitter at effector: autonomic: acetylcholine or noradrenaline. Somatic: acetylcholine

Control - autonomic: involuntary, somatic: voluntary

Effect on target organ: autonomic: excitation/inhibition somatic: excitation

Protection of CNS

Bone, meninges, CSF

Bone

Outermost part, cranium houses the brain, spinal cord run through vertebrae

Meninges

3 membranous layers surrounding brain + spinal cord.

Outer layer (dura mater) - tough and fibrous, sticks closely to bones of skull, not so close to vertebrae canal

Middle layer (arachnoid mater) - loose mesh of fibres, looks like spider web

Inner layer (pia mater) - delicate, contains blood vessels, sticks closely to surface of brain and spinal cord

Cerebrospinal fluid

Clear, watery fluid, occupies sub-arachnoid space, circulates through cavities in brain and vertebral canal

CSF functions

Protection: acts as shock absorber

Support: brain floats in cranium, cushioned by CSF

Transport: during circulation, takes nutrients to cells of CNS and carries waste away

Cerebrum

Biggest part of brain, outer surface of grey matter, inner surface of white matter (myelinated axons), deeper inside is basal ganglia (contains nerve cell bodies associated with control of skeletal muscle), separated by fissures or sulci

Cerebral cortex

Wrinkled, outermost layer of gray matter in the cerebrum, folded to increase surface area, contains 70% of all neurons in CNS, rounded ridges called gyri

Corpus callosum

band of nerve fibres at base of longitudinal fissure that connects left + right hemispheres

Cerebrum - function

Mental activities, perception of senses, initiation and control of voluntary muscle contraction.

3 areas of cerebrum

Sensory - interpret impulses from receptors

Motor - control muscular movements

Association - intellectual and emotional processes, memory

Tracts of cerebrum

Tracts - bundle of nerve fibres

3 types:

- Connect various areas of cortex within same hemisphere

- Carry impulses between the left and right hemisphere

- Connect cortex to other parts of brain or to spinal cord

Cerebellum

Under rear of cerebrum, parallel folded ridges on surfaces, grey matter on outside white matter inside, controls posture, balance, coordination, skeletal control

Hypothalamus

Maintain homeostasis by regulating:

ANS, body temp, food/water intake, waking/sleeping cycle, contraction of bladder, emotional response

Medulla oblongata

Continuation of spinal cord, contains:

Cardiac centre - heart rate, force of heartbeat

Respiratory centres - breathing rate and depth

Vasomotor centre - diameter of blood vessels

Spinal cord

Cylindrical structure consisting of white (contains tracts) and gray matter (on inside, contains nerve cell bodies)

Ascending tracts

Carry sensory information from PNS to CNS

Descending tracts

Carry motor information from CNS to PNS and muscles

PNS structures

Cranial nerves - 12 pairs, most are mixed (contains fibres that carry impulses away and fibres that carry impulses to brain)

Spinal nerves - 31 pairs that arise from spinal cord, all are mixed nerves, nerves join to spinal cord via 2 roots

Ventral root

carries motor neurons

Dorsal root

carries sensory neurons