Module 3: Nerve and Muscle Flashcards
Two parts of nervous system
Central nervous system
Peripheral nervous system
What makes up the CNS? (2)
Brain and spinal cord
What makes up the PNS? (2)
Peripheral nerves
Ganglia
Which cells make up the CNS and PNS? (2)
Neurons and glia
What are neurons specialised for?
Transmission of information
Main function of glial cells
Provide support for neurons
Dendrite functions (2)
Receive input
Send information to cell body
Where are the organelles in an axon?
In the cell body
Cell body function
Sums inputs
Axon function
Carries action potentials
Axon hillock location and function
Where head meets axon
Initiates action potential
Axon terminal function
Release neurotransmitters
Nucleus (CNS)
Group of cell bodies in the CNS
Tract (CNS)
Bundle of axons in the CNS
Grey matter
Group of cell bodies in spinal cord or cerebral cortex
White matter
Bundle of axons in spinal cord or cerebral fluid
Ganglion
Group of cell bodies in the PNS
Nerve
Bundle of axons in the PNS
What are the four neuron components/ zones?
Input zone
Summation zone
Conduction zone
Output zone
Input zone
Dendrites and cell body
Receives chemical signals from other neurons
Summation zone
Axon hillock
Summation of inputs
Conduction zone
Axon
Carries action potentials
Where does the axon carry action potentials between? (4)
Between brain areas
To and form spinal cord
From peripheral sensory receptors
To effector cells
Output zones
Axon terminals
In contact with input zone of effectors or other neurons. Releases neurotransmitters
What is a neurotransmitter a type of?
Chemical signal
Name the four neuron types
Multipolar
Bipolar
Unipolar
Anaxonic
Multipolar neuron
Neuron with multiple processes emanating from cell body
Bipolar neuron
Neuron with two processes emanating from cell body
Unipolar neuron
Neuron with one process emanating from cell body.
This process branches into a dendrite and an axon
Anaxonic neuron
A neuron with no distinct axon. All processes look alike
Five types of glial cells
Astrocytes
Microglia
Ependymal cells
Oligodendrocytes
Schwann cells (PNS)
Astrocyte functions (3)
Supply nutrients to neurons
Ensheath blood capillaries
Respond to injury
Microglia function
Engulf microorganisms and debris
Immune cells of the CNS
Ependymal cell function
What special component do they contain?
Line fluid-filled spaces of the brain and spinal cord
Cilia
Oligodendrocyte function
Support axons by ensheathing them with myelin sheath
Schwann cell function
Support peripheral nerve fibres by ensheathing them with myelin
How do Schwann cells ensheath the axon? What tissue is used?
Wrap their plasma membrane around the axon.
Fat (phospholipid)
Which two glial cells are similar in function?
Oligodendrocytes and Schwann cells
What are the gaps between myelin called? What effect do these have?
Nodes of Ranvier
Help to increase conduction
Synapse
A junction where communication between neurons occurs
Where does the axon potential travel to/from?
From axon hillock to axon terminal
What happens after action potential reached axon terminal?
Synaptic vesicles containing neurotransmitter fuse with the membrane and release it into the synaptic cleft
At what point is the neurotransmitter transmitted to the post-synaptic neuron?
At the input zone receptors
How does the signal change during communication between neurons?
Electrical to chemical to electrical
Action potential to neurotransmitter to action potential
Synaptic cleft
Small space between axon terminal of pre-synaptic cell and dendrites of post-synaptic cell
Synaptic vesicle
Vesicle containing neurotransmitter which waits for a signal to release it
What is the cell releasing neurotransmitter called?
Pre-synaptic neuron
What is the cell receiving neurotransmitter called?
Post-synaptic neuron
Afferent information
Information coming into the brain
Efferent information
Response that comes out of the brain
How do we remember the difference between afferent and efferent?
Afferent is information ascending up to the brain
Somatic information
Information we are aware or/ have control over
E.g. voluntary muscle control
Autonomic information
Information we have no awareness of/ body oversees automatically
E.g. blood pressure
Effectors of somatic efferent division
Skeletal muscle fibres
Somatic efferent diversion neurons
Upper motor neuron
Lower motor neuron
Position of upper motor neuron
Cell body in brain
Axon in spinal cord
Position of lower motor neuron
Cell body in spinal cord
Axon in spinal nerve
Similarity between upper and lower motor neurons
Both are myelinated
Where is the first synapse located in somatic efferent division?
In spinal cord
Where is the second synapse located in somatic efferent division?
Between lower motor neuron and skeletal muscle fibres
Which neurotransmitter do somatic efferent division synapses release?
ACh acetylcholine
Two divisions of the autonomic efferent nervous system
Sympathetic and parasympathetic
Effectors of autonomic efferent nervous system (4)
Smooth muscle
Cardiac muscle
Glands
Adipose tissue
How many neurons are used in autonomic efferent pathway?
Three
Positions of neurons in autonomic efferent pathway
- Cell body in brain, axon in brain or spinal cord
- Cell body in brain or spinal cord, axon in PNS
- Cell body and axon in PNS
Are autonomic efferent pathway neurons 2 and 3 myelinated?
2 is, 3 isn’t
Where is the synapse between neurons 2 and 3 in the autonomic efferent pathway?
In an autonomic ganglion
Where is the synapse between neuron 3 and effector in the autonomic efferent pathway?
On effector
How can we refer to neurons about an autonomic ganglion? (2)
Pre-ganglionic neuron
Post-ganglionic neuron
Which neurotransmitter does the first synapse in autonomic efferent pathways release?
Acetylcholine ACh
Which neurotransmitter does the second synapse in autonomic efferent pathways release?
Acetylcholine ACh in parasympathetic division
Norepinephrine NE/ nonadrenaline
Which system does the term ‘fight or flight’ refer to?
Sympathetic division
Which division does the term ‘test and digest’ refer to?
Parasympathetic
Which factors increase and decrease in the sympathetic division?
Increase: heart rate, pupil size, sweating
Decrease: gastric motility, salivation
Which factors increase and decrease in the parasympathetic division?
Decrease: heart rate, pupil size, sweating
Increase: gastric motility, salivation
In which levels of the spinal cord do cell bodies of sympathetic neurons (second) lie?
Thoracolumbar levels
T1-L2
In which spinal cord levels do the cell bodies of parasympathetic neurons (second) lie?
Cranial and sacral levels
Where so sympathetic ganglia lie?
On either side of vertebral column
Where do parasympathetic ganglia lie?
Synapse in or near effector
Which division has a short second axon?
Sympathetic
Which division has a long second axon?
Parasympathetic
Membrane potential
Distribution of ions inside and outside the cell which creates a difference in charge across the membrane
Resting membrane potential
-70mV
Mechanisms maintaining resting potential (2)
Leak channels (potassium and sodium)
Voltage gated channels (potassium and sodium)
What lies at the initial segment of the axon?
High concentration of sodium channels
Where is it decided if AP propagation will go ahead or not?
Axon initial segment
Gates of ion channels (2) and when they open and close
Activation gate: opens when action potential arrives (closer before)
Inactivation gate: closes after depolarisation (open before)
Step one of action potential (at threshold)
A local change in membrane potential occurs sufficient to depolarise the cell
Na+ channels open
Step two of AP
Na+ channels are open and slow Na+ into the cell
Depolarisation occurs
Step three of AP
Na+ channels close
K+ channels open
Repolarisation occurs
Step 4 of AP
K+ channels close
Membrane hyperpolarises because K+ channels are slower to close.
Potential returns to resting and both channels close
Absolute refractory period
Interval of time in which a second action potential absolutely cannot be initiated
Occurs during depolarisation and repolarisation (steps 2 and 3)
Relative refractory period
Interval of time in which a second AP can be generated, but it requires a much larger stimulus than the first AP.
Occurs during hyperpolarisation (step 4)