How many pairs of nerves arise from the brain and spine?
12 cranial nerves
31 spinal nerves (8C, 12T, 5L, 5S, 1C)
There are two types of peripheral motor nerves - somatic and autonomic. What is another term for autonomic?
How is sensory info transmitted from internal organs?
Via visceral afferent fibres
Name all 12 cranial nerves
Olfactory, optic, occulomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal
What is the transmitter used in the somatic nervous system?
Where does the ultimate control of the autonomic nervous system reside?
Hypothalamus - 'head ganglion of the ANS', maintains homeostasis by regulating autonomic and endocrine systems (and modulating behaviour)
What are neurones?
- the principal specialised cell-type of the nervous system
- responsible for sensory, integrative and motor activities
- approximately 100 billion neurons in the brain
- can be classified as excitatory (often using glutamate as their neurotransmitter) or inhibitory (primarily using gamma-aminobutyric acid/GABA as a neurotransmitter)
What are neuroglia?
- outnumber neurons 10:1, but represent only 50% of the brain volume because they are generally smaller
- main types: astrocytes, oligodendrocytes, microglia (plus Schwann cells in the PNS)
- the term glia comes from the Greek word for glue, but it is now known they offer much more than just structural support to nerve cells
What is a unipolar neurone and where are they found?
Unipolar neurons have a single long process, where the original two processes have fused to become one, so they are also referred to as pseudounipolar.
These include the first order sensory neurons that have cell bodies in the dorsal root ganglia and cranial nerve ganglia.
What is a bipolar neurone and where are they found?
Bipolar neurons have 2 processes coming from the cell body, tend to be found in special sensory structures (e.g. the ear, nose and eye)
What is a multipolar neurone and where are they found?
Multipolar neurons which have numerous processes (called neurites) make up the majority of nerve cells in the brain.
What is an astrocyte?
The main glial cell - star shaped, important for:
- brain energy metabolism
- neurotransmission (constant ionic env)
- detoxification of ammonia
- inflammation and repair
- learning and memory (?)
- blood-brain barrier (BBB)
Why do neurones prefer lactate to glucose and how do astrocytes contribute to this?
Neurones prefer lactate as energy extraction from this substrate produces less oxidative stress which can potentially harm nerve cells because they are so active.
The astrocytes 'pre-digest' lactate (metabolic coupling).
What is the blood-brain barrier?
Highly selective permeability barrier that separates the circulating blood from the brain extracellular fluid in the central nervous system (CNS).
Lots of tight junctions between capillary endothelial cells in the brain, spinal cord and retina which restrict extracellular passage of molecules. This is due to an inductive interaction between astrocytic feet processes (end feet) which induce changes in the capillary endothelial cells.
What are microglial cells?
- Resident immune and phagocytic cells of the CNS
- Derived from the bone marrow
- Related to monocytes and macrophages
- immune responses
- removing dead cells / debris (by phagocytosis)
- immune responses
- removing dead cells / debris (by phagocytosis)
What are microglial nodules?
Clusters of activated microglia also surround and destroy nerve cells that have been infected by viruses and must be sacrificed.
What is neuronophagia?
the process by which the microglial cells digest the dead neurons
What are oligodendrocytes?
Responsible for myelination of CNS axons. Provide multiple cytoplasmic processes that extend to several neighbouring axons and provide a single myelin segment to each of them.
Analogous to Schwann cells in the peripheral nervous system. Degenerate in demyelinating disorders such as multiple sclerosis
What is grey matter?
Grey matter consists of neuronal cell bodies, dendrites, synaptic connections and glial cells, especially astrocytes.
What are the two main types of grey matter?
- superficial layer of grey matter (2-4mm thick)
- forms the superficial surface of the brain
- has six layers in most areas
- collections of neuronal cell bodies in the CNS
- buried in hemispheric white matter / brain stem
- not to be confused with the nuclei inside cells
What is white matter?
White matter is made up of myelinated axons and glial cells, especially oligodendrocytes.
Describe the three main types of subcortical white matter
Association fibres - link areas of the cortex within a cerebral hemisphere
Commisural fibres - link matching areas in the left and right cerebral hemispheres, eg. the corpus callosum.
Projection fibres - either (i) leave the cerebral cortex and project downwards towards the brain stem or spinal cord (eg. corticospinal motor tract) or (ii) project upwards towards the cortex via a synaptic relay in the thalamus (eg. the ascending sensory pathways for touch, pain and temperature are projection fibres). The large bundle of projection fibres that passes between the basal ganglia and thalamus is the internal capsule
Why is the internal capsule clinically important?
as damage here (e.g. due to a stroke) may cause contralateral paralysis or sensory loss by interrupting the motor and sensory projection fibres
What is the cerebrum responsible for?
The cerebrum is responsible for sensation, movement, thought, behaviour, personality, language, memory and learning. Diseases of the cerebral hemispheres (e.g. stroke, tumours) can therefore affect any of these functions. The cerebral hemispheres are linked across the midline by the corpus callosum, which is a massive bundle of around 300 million nerve fibres.
What is the cerebellum responsible for?
The cerebellum is involved in the control of balance, posture, muscle tone, coordination and dexterity (including fine control of the tongue muscles). Disease in this part of the brain therefore leads to clumsiness, erratic motor control (called ataxia) and slurred speech (called dysarthria). Some types of learning probably also rely on the cerebellum, most probably the acquisition of complex motor skills (e.g. learning to juggle, play the piano or touch-type).
What is the brainstem responsible for?
The brain stem is involved in “life support” functions including the regulation of breathing, control of the heart rate and blood pressure, airway-protective reflexes (e.g. cough, sneeze, gag) that help to prevent choking and inhalation of fluids (aspiration) which can cause pneumonia. The brain stem is also critical for maintaining wakefulness (consciousness) and regulating normal sleep-wake cycles. Brain stem damage may therefore result in coma or death.
What is the frontal lobe important for?
Contains the primary motor cortex and is therefore important for movement (but also behaviour and language).
What is the temporal lobe important for?
Contains the primary auditory cortex and is important for hearing
What is the occipital lobe important for?
The primary visual cortex
What is the parietal lobe important for?
in sensations of touch and pain but also contributes to visuospatial ability