Chapter 4 - Nervous systems

CNS and PNS

CNS is made from

• Brain - memory, reasoning, conscious movements 

• Spinal cord - reflexes, transmit signal to and from brain 

PNS consists of

Nerve + Ganglia 

Afferent division (Sensory)

Efferent division (Motor Efferent) ME

Afferent division

Carry nerve impulse into the CNS

• Visceral sensory (Signals from internal organs)

• Somatic sensory (Signals from skin, muscle and external stimuli)

Efferent division

Carry nerve impulse away from the CNS to

• Somatic NS - skeletal muscles and regulates conscious response, complete control (always excitation)

• Autonomic NS - smooth muscles, cardiac muscles and glands

• regulates involuntary response

• excitation and inhibition 

Autonomic nervous system 

Carries NI away from the CNS to smooth muscles, cardiac muscles and glands (involuntary)

• Sympathetic division - fight or flight

• Parasympathetic - rest and digest

Protection of the CNS 

• Bones 

• Meninges 

• Cerebrospinal fluid 

Bones

• Cranium - part of the skull that protects the brain

• Vertebrae - protects the spinal cord

STRONG, RIGID structure to protect

against DIRECT, HARD, IMPACT

Meninges consists of

• Dura mater (Outer)

• Arachnoid mater (Middle)

• Pia mater (Inner)

Meninges is found inside the 

• bones 

• covering surface of brain 

• Spinal cord 

Dura mater (Brain)

• Tough and fibrous layer

• Laid flush against the cranium

• Holds the brain in place

Dura mater (Spinal cord)

• On the inside of the vertebral canal there is a space containing, fat, connective tissue and blood vessels - serve as padding and allow the spinal cord to bend

Arachnoid mater

loose mesh of fibres (connect the DM and PM)

Pia mater 

inner meningeal layer: sticks closely to the surface of the brain and spinal cord 

• Delicate layer 

• laid flush against the cerebral cortex 

• prevents the entry of pathogens 

Cerebrospinal fluid

Clear, watery fluid containing protein, urea, glucose and salts (PUGS)

• Between middle and inner layer of meninges

• Cavities in the brain and through a canal in the centre of the spinal cord

Brain suspended in clear, watery fluid

• absorbs shock

• and dissipates the energy from the impact

Cerebrospinal fluid functions: (SPT)

• Support - Brain is suspended inside the cranium and floats in the fluid that surrounds it

• Protection - shock absorber and dissipates energy

• Transport - takes nutrients to the cells of the brain and SC and carries away their waste

CNS consists of

1. Outer grey matter - Dendrites, unmyelinated fibres, Nerve cell bodies (DUN) 

2. Inner white matter - myelinated fibres 

tract is

bundle of nerves (white matter)

Parts of the brain

1. Cerebrum

2. Cerebellum

3. Medulla oblongata

4. Hypothalamus

5. Corpus callosum

Cerebrum

Biggest part of the brain that consists of

• Outer surface of grey matter - cerebral cortex

• Grey matter deep inside the cerebrum - basal ganglia

• Inner white matter

Cerebral cortex - outer grey matter 

• Greatly folded to increase SA for a large number of neurons - convolutions 

• Folding produces rounded ridges called convolutions = gyrus 

• Shallow downfolds - sulcus 

• Deep downfolds - fissures 

Longitudinal fissure

deepest fissure

• splits the cerebrum into 2 halves, the left and right cerebral hemisphere

Lobes of the cerebrum (FITOP)

Frontal lobe MUST GIVE EXAMPLE

• Higher-order function - problem solving skills 

• Complex decision making 

• Initiate skeletal muscle movement 

Broca’s area speech production

Parietal lobe 

Process temperature, touch, taste, pain and movement - sensory information

Temporal lobe 

Process memories and link with senses 

• receives auditory information

Wernicke’s area speech comprehension 

Occipital lobe

Vision, interpretation of signals from eyes

Insula

Recognition of different senses and emotions, addiction and psychiatric disorders

Cerebral cortex function 

Involved in mental activities such as thinking, reasoning, learning, memory intelligence and sense of responsibility 

• perception of senses 

• initiation and control of voluntary muscle contraction 

Functional areas in cerebral cortex

1. Sensory area - interpret impulses from receptors

2. Motor area - control muscular movement

3. Association area - concerned with intellectual and emotional processes

Association area of cerebral cortex is involved with

Memory

• memories are not stored in indivdual memory cells instead they are a pathway of neurons

• when a memory is stored, new links are made between neurons or existing links are modified

Basal ganglia - inner grey matter deep inside each hemisphere 

Consists of 

• a group of nerve cell bodies associated with the control of skeletal muscles 

Inner white matter

Consists of myelinated fibres has 3 tracts

• connect various areas of the cortex within the SAME hemisphere

• carry impulse BETWEEN the left and right hemisphere

• connect cortex to other parts of the brain and spinal cord

Corpus callosum

Bundle of nerve fibres (tract) that lie underneath the cerebrum at the base of the longitudinal fissure

• composed of myelinated fibres

Function: allow the right and left hemisphere to communicate

Cerebellum 

Lies under rear part of the cerebrum 

• surface folded into a series of parallel ridges 

• Outer folded part - grey matter 

• Inside is white matter branches to all parts of the cerebellum 

Function: control posture, balance and fine coordination of voluntary muscles 

• Smoothen out skeletal muscle movement 

What happens if the cerebellum is damaged/removed

functions take place below the conscious level

• Jerky

• Spasmodic

• Uncontrolled

Hypothalamus

Lies in the middle of the brain, controls many body activites but mainly HOMEOSTASIS

The hypothalamus regulates

• Core body temperature

• Patterns of waking and sleeping

• Secretion of hormones

Medulla Oblongata 

Contains 

• Cardiac centre - regulates rate and force of heartbeat 

• Respiratory centre - control rate and depth of breathing 

• Vasomotor centre - regulates diameter of arteries/arterioles 

also regulates reflexes of swallowing, sneezing, coughing and vomitting

All the centres are controlled by the hypothalamus

Spinal cord 

Ascending tract - sensory axons that carry impulse towards the brain 

Descending tract - motor axons that carry impulse downwards away from the brain 

Function:

• Carry sensory impulse up to the brain and motor impulse down the brain 

• integrate certain reflexes 

Ganglia

group of nerve cell bodies outside the CNS

Cranial nerves

12 pairs of nerves arise from the brain

• most are mixed nerves (contains sensory and motor fibres)

• a few only carry sensory impulse or motor impulse

Spinal nerves 

31 pairs of nerves arise from the spinal cord 

• ALL are mixed nerves joined to the spinal cord by the dorsal and ventral root 

Ventral root

contains the axons of motor neurons that have their cell body in the grey matter of the spinal cord

Dorsal root

Contains sensory axons that have their cell bodies in a small swelling on the dorsal root —> dorsal root ganglion

Autonomic pathway 

• 2 motor neurons from CNS to effector (involuntary muscles, cardiac muscles and glands)

• Synapse in ganglion 

• NT: acetylcholine / noradrenaline 

Somatic pathway

• one motor neuron

• carry NI to effector (skeletal muscles)

• NT: acetylcholine

Autonomic nervous system receive two sets of nerve fibres

Sympathetic fibres: prepare for strenuous activity - fight or flight

• noradrenaline

Parasympathetic fibres: maintain body during rest and digest

• acetylcholine