Mammalian Physiology- The Brain

Organisation

• Made up of neurones and glial cells
• Neurones transmit info. in the form of action potentials
• Glial cells help nutrients from blood to neurones, maintains correct ionic balance in tissue fluid surrounding, destroy pathogens by phagocytosis. Schwann cells (myelinated sheath) are glial cells

Central Nervous System

• Includes the brain and the spinal cord
• Most neurones are intermediate with short dendrites and many synapses. Some synapses are excitatory (AP arrives and depolarises postsynaptic membrane). Some synapses are inhibitory (prevents post-synaptic membrane from depolarising).
• Spinal cord extends from base of brain to 1st lumbar vertebrae. In the centre is a canal containing cerebrospinal fluid.

• The brain is a highly specialised extension of the spinal cord
• Both the brain and the spinal cord are surrounded by three membranes called meninges. They help to secrete cerebrospinal fluid. The fluid helps to absorb mechanical shocks to the brain.

Peripheral Nervous System

• Made up of sensory neurones (AP from receptors to CNS) and motor neurones (AP from CNS to effectors)
• Sensory neurones- cell bodies found outside spinal cord and in the dorsal root ganglia. Long cytoplasmic axons to get info. from receptors. Receptors the transmit AP to cell bodies where AP passes along axons to the CNS.
• Motor neurones- cell bodies found in the spinal cord. Long axons pass out of the spinal cord towards the effectors.
• In the PNS axons and dendrons arranged in bundles called nerves. They enter and leave the CNS in spinal nerves which occur between vertebrae.
• Each spinal nerve has a dorsal root and a ventral root

• Includes all of the motor neurones that take info. to internal organs
• Different function and organisation to somatic system
• Cell bodies of motor neurones in autonomic system have cell bodies outside of CNS in the autonomic ganglia. The preganglionic neurone carries info. (AP) to this ganglion from the CNS

Sympathetic Nervous System- "fight or flight"

• From the ganglia in the autonomic ganglia, axons pass to all organs in the body forming synapses with muscles. Transmitter substances at these substances is noradrenaline-"stimulates organs"
• Some neurones in sympathetic release ACh as neurotransmitter

Parasympathetic Nervous System- "rest and digest"

• Nerve pathways all begin in the brain- neurotransmitter is ACh
• The motor neurone keeps on going until it synapses when actually in the wall or the muscle/organ itself. Synapses with effector neurone
• Most axons are found in the vagus nerve

• Contains ventricles filled with cerebrospinal fluid
• Consists of myelinated areas (white) and unmyelinated (grey)
• Cerebrum (frontal lobe) is split into left and right cerebral hemispheres which are linked by the corpus callosum
• Cerebral hemispheres covered by a highly folded layer called the cerebral cortex
• Diencephalon- made up of the thalamus and hypothalamus
• Behind and beneath the thalamus lies the midbrain, and above this is the cerebellum. There cerebellum has a folded surface and is devided into lobes
• Beneath this is the medulla oblongata

• "higher order" processes, i.e. thinking/language/memory and emotions
• the cerebral cortex of both cerebral hemispheres receives sensory info. from sense organs (eyes/ears) hence the name sensory areas
• Parts of the cortex that 1st receive info. are primary sensory areas. The other areas that receive impulses and integrate info. from primary areas and called association areas
• the different areas of the cerebral cortex must interact to carry out our thought or actions

• hypothalamus receives a wide range of info. then responds using autonomic system or pituitary gland
• control of endocrine glands --> pituitary gland. Secretions from posterior pituitary gland controlled by neurones which secret the hormone itself. These hormones include anti-diuretic hormone (water reabsorption) and oxytocin (uterus contraction)
• Secretions from anterior pituitary gland. Neurones in the hypothalamus produce different hormones and secret into surrounding vessels --> neurosecretion
• Hormones are carried to APG where they effect the production and release of other hormones. If they stimulate this they are called releasing hormones, opposite are called inhibiting hormones.

• The Cerebellum is concerned with the control and co-ordination of movement and posture
• It receives inputs from all other parts of the CNS/Sensory neurones. This info. is integrated and sent to motor neurones of the cerebellum
• The cerebellum helps to compensate for small errors in movement and is involved in the learning of tasks requiring co-ordinated movements, i.e. racket sports

• the medulla oblongata is responsible for the control of breathing, heart rate and blood pressure
• Groups of neurones produce rythmic patterns of impulses which pass along the vagus nerve to the diaphragm/intercostal muscles
• this breathing pattern can be modified by changes in CO2 concentration. If it rises then receptor cells in the medulla oblongata detect this and neurones respond by increasing frequency of impulses sent to breathing muscles
• A different part of the medulla oblongata contains neurones that are responsible for regulating heart rate and blood pressure. Receives info. about blood pressure from baro recepetors and info about CO2 conc. . Neurones take impulses from medulla oblongata to the sino-atrial node in the right atrium
• If blood pressure is low or too much CO2 in blood then the medulla oblongata sends impulses along neurones that are part of sympathetic system and causes the SAN to beat faster
• High blood pressure --> vagus nerve --> SAN beats slowly

Symptoms: Tangles (bundles of fibres)/Plaques (dark deposits). Reduction in brains size, concentration is more difficult, changing patterns of behaviour, anxiety increases, increasing loss of memory, hallucinations

Causes: Don't know! Tangles are made of a protein called Tau. As tau builds up in neurones they die. Plaques contain portein called beta amyloid (AB). Its precursor is APP (always found in membranes). AB is secreted by normal cells throughout life. Plaques form when there is more AB secreted than normal or when a person has AB42 rather than AB40.

Also evidence for genes which code for APOe. Increases rate at which AB is deposited.

Ageing increases risk. Also smoking/high cholesterol levels

Prevention/Treatment: Drugs which temporarily reduce symptoms. Use brains regularly/exercise/good diet