Central Nervous System

What does the CNS consist of?

• brain

• spinal cord

Incoming and outgoing messages processed here.

What protects the CNS?

• bone

• membranes called meninges

• cereborspinal fluid

What is the outermost protective layer for the brain and spinal cord? Why?

Bone:

• brain = cranium

• spinal cord = vertebral canal (opening in the vertebrea, spinal cord runs through)

Provides a strong, rigid structure to protect the structures underneath

What are meninges?

three layers of connective tissue forming membranes that cover the surface of the brain and spinal cord

What are three layers connective tissue in the meninges?

• Dura mater (outer layer), tough and fiborous and provides a protection layer for the brain

• Arachnoid mater (middle layer), a loose mesh of fibres

• Pia mater (inner layer), delicate (contain many blood vessels) and sticks closely to surface of the brain and spinal cord

Where is cerebrospinal fluid?

occupies space between middle and inner layer of meninges, also circulates through the cavities of the brain and through a canal in the centre of the spinal cord

What is cerebrospinal fluid?

clear, watery fluid containing a few cells + some glucose, proteinm urea and salts

What are the 3 functions of cerebrospinal fluid?

• protection: acts as a shock absorber

• support: the brain is suspended inside the cranium (floats in the fluid that surrounds it)

• transport: CSF is formed in the blood and circulates around through the CNS before eventually re-entering the blood capillaries, during circulation takes nutrients to the cells of the brain and spinal cord and carries away waste

What is the brain?

a very complex organ, both in structure and function

What is the cerebrum? What is the matter composition?

• largest part of the brain

• consists of grey matter 2-4mm thick (outer surface), known as cerebal cortex

  • consists of neuron cell bodies, dendrites, unmyelinated axons

• white matter (below the surface of the cortex)

  • made up of myelinated axons

• deep inside is additional grey matter (basal ganglia)

Is the cerebrum smooth or folded?

• folded in patterns to increase surface area

  • contains 70% of all neurons in the CNS

  • folding produces rounded ridges (convolusions)

    • convolutions seperated either by sulci (shallow downfolds) or fissures (deep downfolds)

What does the longitudional fissure do?

• deepest fissure, almost seperates cerebum in half

  • left + right cerebal hemispheres

What is the Corpus Callosum?

• base of longitudinal fissure joining the 2 hemispheres is area of white matter consisting of a large bundle of transverse fibres known as the Corpus Callosum

How many lobes is the cerebal hemisphere divided into?

• 5 lobes

  • frontal, temporal, occipital, patietal, insula (deep inside brain)

What is the cerebal cortex involved in?

• thining, reasoning, learning, intelligence, memory

• perception of senses, iniation of volunatary muscle contraction

What is the frontal lobe involved in?

thinking, problem solving, emotions, personality, language, control of movement

What is the parietal lobe involved in?

processing temperature, touch, taste, pain, movement

What is the temporal lobe involved in?

processing memories and linking them with senses; recieves auditory information

What is the occiptal lobe involved in?

vision

What is the insula lobe involved in?

recognition of different senses + emotions, addiction and psychiatric disorders

What 3 functional areas can the cerebral cortex be broken into?

• sensory - interpret impulses from receptors

• association - intellectual + emotional processes

• motor - control muscular movements

What is one of the important functions of the cerebrum?

memory

• The association areas involved in memory

• Memories are not stored in individual memory cells in the brain: they are pathways of nerve cells

  • memory is stored = new links are made between neurons or existing links are modified

Are the two hemispheres similar?

Appear similar, but are not (have specialised functions).

• right-handed people:

  • right frontal lobe is wider than the left

  • left occipital and parietal lobes are wider than the right ones

• Language ability: normally left hemisphere

• musical and artistic abilities: right hemisphere

What is the corpus callosum?

a wide band of nerve fibres that lies underneath the cerebrum at the base of the longitudinal fissure. Nerve fibres in the corpus callosum cross from one cerebral hemisphere to the other and allow the two sides of the cerebrum to communicate with each other.

Where is the cerebellum located?

• lies under rear part of the cerebrum

• second largest part of the brain and its surface is folded into a series of parallel ridges

What type of matter is the outer folded part of the cerebellum?

outer folded part of the cerebellum is grey matter

What type of matter is the inside part of the cerebellum?

white matter that branches to all parts of the cerebellum, rather like the branches of a tree

What is the cerebrum responsible for?

posture, balance, fine coordination of voluntary muscle contraction

Is the cerebellum under consious control?

No, the cerebellum is not under conscious control

Where is the hypothalamus located?

middle of the brain and cannot be seen from the outside

Is the hypothalamus big?

No, small

What is the hypothalamus mostly concerned with?

Homoestasis

What are the functions of the hypothalamus?

regulation of:

• autonomic nervous system (heart rate, blood pressure, etc.)

• food and water intake

• body temperature

• emotional response (e.g. fear, anger, pleasure)

• patterns of waking and sleeping

• contractions of the urinary bladder

• secretion of hormones and coordination of parts of endocrine system

  • acting through pituitary gland, hypothalamus regulates: metabolism, growth, reproduction, response to stress

What is the medulla oblongata?

a continuation of the spinal cord

How long is medulla oblongata?

~3cm and extend just above the point where the spinal cord enters the skull

What do nerve fibres do in the medulla oblongata?

many nerve fibes simply pass through going to or from other parts of the brain BUT it does have an important role in automatically adjusting body functions

What does the medulla oblongata contain?

• cardiac centre (regulates the rate and force of the heartbeat)

• respiratory centres (control rate and depth of breathing)

• vasomotor centre (regulates the diameter of blood vessels)

Are the centres of the meduall oblongata influenced an controlled by other regions?

Yes, higher centres in the brain, particularly the hypothalamus

What is the spinal cord?

roughly cylindrical structure about 44 cm long in an adult

Where does the spinal cord extend to?

extends from the foramen magnum (large opening at base of skull) to the second lumbar vertebra (about waist level)

How is the spinal cord protected? What allows the spinal cord to bend?

enclosed in the vertebral canal, and inside the ring of bone are the three meningeal layers.

HOWEVER, outmost meningeal layer not joined to bone (unlike how it is joined to the bone in the skull), instead, space containing fat, connective tissue and blood vessels serves as padding around spinal cord and allows the spinal cord to bend when the spine is bent.

How is the grey matter and white matter presented in the spinal cord?

grey matter of the spinal cord is at the centre, surrounded by the white matter

What is the central canal?

a small space found in the cross-bar of the H (grey matter) which runs the length of the spinal cord and contains cerebrospinal fluid

What letter is the grey matter in the spinal cord roughly?

letter H

How is the white matter arranged in the spinal cord?

myelinated nerve fibres of the white matter are arranged in bundles known as ascending and descending tracts.

What are ascending tracts in the spinal cord?

sensory axons that carry impulses upwards, towards the brain

What are descending tracts in the spinal cord?

contain motor axons that conduct impulses downwards, away from the brain

What are the two functions of the spinal cord?

1. carry sensory impulses to the brain and motor impulses away from the brain

2. integrate certain fast, automatic responses (reflexes)