How nerves work Flashcards
Describe the subdivisions of the nervous system.
The central nervous system:
Brain and spinal cord
The peripheral nervous system:
Autonomic - sympathetic, parasympathetic and enteric (involuntary)
Somatic - voluntary
Describe the anatomy of the brain.
The brain is composed of two parts:
Cerebellum - responsible for balance and coordination
Cerebrum - surface is called cerebral cortex, bumps are called gyrus, the grooves between gyri are called sulcus.
Name 4 lobes of the brain and state their purpose.
Frontal lobe = speech and movement (primary motor centre)
Parietal lobe = sensation (somatic sensory cortex)
Temporal lobe = hearing
Occipital lobe = vision
Describe the purpose of the meninges and the 3 different types.
The meninges are why the brain appears to look shiny, the meninges are 3 layers of connective tissue:
- Pia matter, is the deepest and thinnest layer
- Arachnoid is the middle layer.
- Dura matter, most superficial layer, thick tough layer.
Describe the anatomical organisation of the brain and brain stem.
Diencephalon contains the thalamus and hypothalamus (regulation of temperature, thirst and hunger)
Inferior to the diencephalon is the brain stem (regulation of blood pressure, respiratory rate and vomit centre)
Then follows, (inferiorly):
Mid brain
Pons
Medulla oblongata
Then continuous with spinal cord.
Describe the anatomical organisation of the spinal cord.
31 pairs of spinal nerves.
8 cervical
12 Thoracic
5 Lumbar
5 Sacral
1 Coccygeal
Describe the microanatomy of the spinal cord.
The dorsal root contains sensory fibres that carry information from the periphery towards the CNS.
The dorsal root ganglia is where the cell bodies of sensory fibres are contained.
The ventral root contains motor fibres that carry signals away from CNS towards the periphery to give instructions.
Describe white and grey matter in the vertebral column.
White matter is on the outside of the spinal cord contains mostly axons, white colour because some axons are myelinated.
Gray matter is on the inside of the spinal cord and contains all cell bodies that reside in the ventral and dorsal horns.
Describe the general structure of a neuron.
Neurons have a soma (cell body) this contains the nucleus.
Neurons have dendrites that extend from the neuron and receive information.
The “initial segment” or the axon hillock triggers action potentials.
The axon is like a long wire connecting the neuron to all its different parts, it sends the action potential.
The release of the action potential comes at the end of the axon at synapses or ‘presynaptic terminals’.
Describe the morphology of neurons.
Afferent (sensory) neurons can be bipolar or pseudounipolar.
Interneurons can be multipolar or anaxonic (no clear axon).
Motor neurons can be multipolar.
Name the different kinds of Glia in the central nervous system
Astrocytes
Oligodendrites
Microglia
Ependymal cells
Describe astrocytes
Astrocytes are one of the supporting cells in the central nervous system.
They maintain the external environment for neurons, by regulating the water and potassium concentrations in the extracellular fluid.
They also surround blood vessels and form the blood brain barrier.
Describe oligodendrites.
These form myelin sheaths in the central nervous system.
These sheaths are wrapped around axons and can speed up the transmission of a signal.
Describe microglia.
Microglia are the macrophages of the CNS, that hoover up infection (e.g. by phagocytosis).
Describe ependymal cells.
These cells produce the cerebrospinal fluid that surrounds the brain and protects it.
Describe the different types of glia in the peripheral nervous system.
Schwann cells -
These are the (PNS) equivalent of oligodendrites, they form myelin sheaths over axons, however they can only insulate 1 axon.
Satelite cells -
Support cell bodies.
Describe what is meant by a resting membrane potential.
The resting membrane potential of a cell is a state where there is no net flow of ions across the cell membrane. This is important to keep the cell in a state where is it ready to respond.
Describe the ionic basis of the resting membrane potential.
The resting membrane potential is generated by the selective permeability of the resting membrane to K+.
The resting membrane potential is therefore close to the K+ equilibrium potential.
Explain functions of graded potentials.
Graded potentials depolarise the membrane to the threshold value that then allows the firing of an action potential.
Graded potentials can signal stimulus intensity in their amplification.
Describe some properties of graded potentials.
Decremental, graded potentials become smaller as they travel along the membrane, so they are only useful in short distances.
Can be depolarising or hyperpolarising, neurotransmitters can open channels that either depolarise or hyperpolarise the cell, this means they can excite or inhibit a cell.
Can summate, the addition of two synapses that are happening at the same time.
Describe generator potentials.
Generator potentials happen in sensory receptors.
There is a stimulus and ion channels open. This causes depolarisation of the membrane towards the threshold value. This then allows the firing of an action potential.
Describe end-plate potentials.
End-plate potentials happen at neuromuscular junctions.
The action potential is fired out the ventral root, it then travels down the axon towards the synapse at the neuromuscular junction.
After diffusing across junction the action potential reaches the skeletal muscle membrane.
Describe post-synaptic potentials.
Post-synaptic potentials happen at synapses.
The neurotransmitter is release at the presynaptic terminal, where it then diffuses across the synaptic cleft towards the membrane of the post-synaptic cell where it binds to the receptors. This then opens channels, causing depolarisation and eventual firing of an action potential.
Describe pacemaker potentials
Pacemaker potentials occur in the pacemaker tissues of the heart,.
