Nervous system Flashcards
The nervous system is composed of …….. and ………
Neurons and neuroglia
Function of nerves?
They transmit nerve impulses along fibres to other neurons
Three main landmarks of a nerve?
Cell body, axon, dendrites
Neuroglia function?
Variety of functions to protect components of the nervous system
What is the synapse?
A small space between a neuron and the cell it’s communicating with
Nerve impulses cannot jump over this space
So neurotransmitters are released into the synapse and convey the information to the receiving cell
What is the axon hillock?
Where the axon gets bigger before the cell body
What is the soma?
The area of the cell body
Where is the nucleus of a neuron?
In the cell body
What nerves does the central nervous system consist of?
The brain and the spinal cord
What nerves does the peripheral nervous system consist of?
Directs impulses from CNS to sensory organs
The peripheral nervous system is divided into two sub systems which are
The somatic nervous system
The autonomic nervous system
Which branch of the peripheral nervous system controls conscious actions (using skeletal muscle)
Somatic nervous system
Which branch of the peripheral nervous system controls unconscious actions (using smooth and cardiac muscles)
Autonomic nervous system
What are the two branches of the autonomic nervous system?
Sympathetic nervous system
And the parasympathetic nervous system
What does the symoathetic nervous system control?
Actions requiring quick responses (Fight or flight)
Parasympathetic nervous system function
Returns you to normal from sympathetic response (rest and digest)
What are the three neuroglia of the central nervous system?
Microglial cells (phagocytise bacterial cells and cellular debris)
Oligiodendrocytes (form the myelin sheath in brain and spinal cord) (area surrounding the axon)
Astrocytes (between blood vessels and neurons for support, nutrients and more)
What is the neuroglia type for the peripheral nervous system?
Schwann cells (produce myelin)
Purpose of dendrites?
Carry impulses from other neurons towards cell body
What is at the end of the axons where synaptic knob is?
Axon terminal
What’s the name of axons that are enclosed by a myelin sheath (produced by schwann cells)?
Myelinated fibre
What is the myelin surrounded by on a myelinated fibre?
Neurilemma
What is the name of the gaps between Schwann cells in a myelinated neuron?
Nodes of ranvier
What is white matter made up of in the central nervous system?
Myelinated neurons
What is grey matter in the central nervous system?
Unmyelinated tissue
What do multipolar neurons consist of?
Multiple dendrites, one axon from cell body
These are found in the CNS
What do bipolar neurons consist of?
A single axon and single dendrite extending from each side of the cell body in opposite directions
What do unipolar neurons consist of?
One axon leading from the cell body that divides into two and heads in opposite directions. Found in ganglia of the CNS
What are sensory neurons?
Afferent neurons which conduct impulses from peripheral receptors to CNS (usually uni polar)
Overlap between peripheral and central nervous system
What are interneurons?
Multipolar neurons in the CNS forming links between other neurons
What are motor neurons?
(Efferent neurons) multipolar neurons that conduct impulses from CNS to effectors
Order of effect starting at sensory receptor to effector
Sensory receptor (peripheral NS) —-> sensory neuron (peripheral into central NS) —————> interneuron (CNS) ————> interneuron (in another part of CNS) ———> motor neuron (CNS into peripheral NS) ———-> effector
What is the name of the junction between two communicating neurons?
The synapse
What area of the synapse must the impulse be conveyed across?
Synaptic cleft
What is the name of the neuron sending the impulse (before the synapse)? What is the name of the neuron receiving the impulse (after the synapse)?
Before synapse =presynaptic neuron
After synapse= postsynaptic neuron
What carry the message of the impulse in synaptic transmission?
Neurotransmitters
Which end of the axons gave synaptic knobs?
Distal end of axon
What do synaptic knobs contain are filled with neurotransmitters?
Synaptic vesicles
What is the result of an Excitatory action from neurotransmitter?
The likelihood of an action potential is increased (action potential causes neurotransmitters to be released from postsynaptic neuron to carry on the nerve signal)
What is the result of an inhibitory action of neurotransmitters?
The likelihood of an action potential is decreased making it less likely for postsynaptic neuron to release neurotransmitters and continue the nerve impulse
If a cell membrane is polarised where is there an excess of negatively charged ions?
On the inside of the membrane
What does depolarisation involve?
The movement of charged ions out of the membrane to equalise the charge between the inside and the outside of the membrane
Sodium-potassium ion pumps move what ions in and out of the membrane?
Moves potassium ions into the membrane more readily than it moves sodium ions into the membrane. Causing more potassium ions on the inside and more sodium ions on the outside of the membrane.
What is the gate-like channel in the membrane which facilitates the movement of charged ions?
A protein
Are sodium ions and potassium ions positively charged of negatively charged?
Both positively charged
If both sodium and potassium ions are positively charged, how is there a negative charge outside the membrane?
Because more potassium ions are pumped into the membrane than sodium ions pumped out so in comparison to the inside of the membrane, the outside is more negatively charged (has less positive)
The movement of sodium ions out and potassium ions in maintains what?
A resting potential
What is a resting potential and what is its value?
This is the separation of charge (potential difference) between the outside of the membrane and the inside of the membrane.
The value is -70 MV
What happens when a membrane is stimulated by neurotransmitters?
The membrane potential changes, becoming less negative (smaller potential difference) becoming depolarised
If enough depolarisation occurs, what is reached and what happens?
A threshold potential is reached causing more ion channels to open. This causes a flood of ions and an action potential is reached
How is an action potential reached?
A change in potential difference causes threshold potential to be reached. This changes the membrane permeability to sodium at the axon hillock (the trigger zone).
Sodium ions rush in, depolarising the membrane potential.
Potassium channels allow potassium ions to leave the cell and the membrane is repolarised as the resting potential is reestablished. This sequence is an action potentional.
What happens when the call membrane becomes repolarised as sodium ions move back in and potassium ions move back out?
The resting potential is reestablished (-70mV)
After an action potential what happens?
A bioelectrical current flows along axon down the fibre that stimulates the next region
Where does the action potential occur?
In and along the axon (regions of the axon one by one)
Order of events for action potential?
Resting potential maintained by ion pump (-70mV)
Threshold stimulus is received
Sodium channels in trigger zone open
Sodium ions move in by diffusion (depolarising membrane)
Potassium ions channels open potassium ions move out- repolarisation
Action potential
Bioelectrical current stimulates next region of axon until axon terminal
What is saltatory conduction?
The movement of nerve impulse in myelinated neurons from one node of ranvier to the next (jumping) = faster conduction
What factors other than myelination affect speed of conduction?
Length of axon
Thickness of axon
How is conduction an all or nothing response?
As long as the nerve stimulation by neurotransmitters causes depolarisation to reach the threshold potential, the sequence occurs and an action potential is caused, if it does not reach the threshold potential, there is no action potential, it doesn’t matter how far over or under the action potential the stimulus goes, the result is still the same because all action potentials are the same strength
What is the refractory period?
Short ‘recovery’ period of time after action potential where a threshold stimulus will not trigger another action potential
Result of refractory period
Frequency is limited
Ensures impulse is only transmitted in one direction (down axon towards terminal)
What causes neurotransmitters to be released from synaptic vesicles?
Biochemical current of action potential spreads over synaptic knob.
Synaptic knob becomes more permeable to calcium
In presence of calcium, synaptic vesicles fuse to synaptic knob membrane
Then synaptic vesicles release neurotransmitters into synaptic cleft
What do enzymes in synaptic cleft do after the release of neurotransmitters
Break down and decompose neurotransmitters to prevent continuous stimulation of postsynaptic neuron
What enzyme breaks down acetylcholine neurotransmitter?
Acetylcholinesterase
Why are the three types of nerves?
Sensory (afferent) nerves- bring info to CNS
Motor (efferent) nerves- carry impulses from CNS to effectors
Mixed nerves- carry sensory and motor fibres
What is the name of a bundle of nerve fibres held together by layers of connective tissue?
A nerve
The name of the outer covering of a nerve
Epineurium
The name of the covering of fascicles of nerve fibres?
Perineurium
The name of the covering of individual nerve fibres
Endoneurium
What is a reflex arc?
When a receptor detects change in environment a sensory neuron carries info to CNS
An inter neuron in CNS carries info to motor neuron
Motor neuron carries response to effectors
Effector responds to change
What are reflexes?
Automatic responses to change in environment in or out of the body by stimuli. To help maintain homeostasis
The name of membranes surrounding the brain and spinal cord between bone and soft tissue?
Meninges
What is the name of the outermost meninx, containing many blood vessels?
Dura mater
Which meninx forms the inner periosteum of the skull bones?
Dura mater
The name of the space that separates the sheath around the spinal cord from the vertebrae?
Epidural space
Three cranial meninges and locations
Falx cerebelli, under occipital bone
Falx cerebri, brow to occipital bone
Tentorium cerebelli, temporal bone
Three meninges in the spinal cord?
Inner- dura mater
Middle- arachnoid mater
Outer- pia mater
Where does the spinal cord begin and end?
Begins at base of brain and ends to the intervertebral disc between first and second lumbar vertebrae
Upper region, middle region, lower region, region in sacrum and region in coccyx of spinal cord
Cervical region Thoracic region Lumbar region Sacral region Coccygeal region
What does the spinal nerve branch into?
Dorsal root (and dorsal rootlets) starting from dorsal root gangion from spinal nerve Ventral root (and ventral rootlets) starting at spinal nerve Either side of spine bone
Which is the name of the largest portion of the brain?
Cerebrum
Which area of the brain consists of lobes under each major skull bone named the same as the bone?
Eg occipital lobe under occipital bone
Cerebrum
Purpose of the hypothalamus?
Maintains homeostasis by regulating activities and linking the endocrine system with the nervous system
Eg blood pressure, body temp, blood water conc, digestion, sleepiness
Where is the cerebellum located
Beneath posterior part of cerebrum
What is the purpose of the corpus callosum?
It links the two cerebral hemispheres
What is the purpose of the cerebellum?
Voluntary muscle coordination
What is the function of the diencephalon?
Processes sensory information
What is the purpose of the brain stem?
It connects the brain with the rest of the body and controls basic life systems such as breathing
Myelin sheath in peripheral NS is formed by?
Myelin sheath in CNS formed by?
Schwann cells
Oligodendrocytes
If the stimulus at the axon terminal is sub- threshold, what affect will this have on the action potential
It will not reverse the membrane signal and cause action potential to continue
What occurs at the axon hillock?
The impulse is first generated
When a muscle contests, where does the motor nerve action potential arrive at?
Motor end plate
Sequence of events when action potential reaches synapse (7 steps)
1) Action potential at axon terminal reverse membrane potential
2) voltage gated calcium channels open and calcium diffuses in
3) vesicles bind to presynaptic membrane
4) neurotransmitter is released across membrane
5) neurotransmitter diffuses across synaptic cleft, binds to postsynaptic receptors
6) sodium channels open , causing action potential of impulse strength is high enough
7) neurotransmitter is broken down and returned to vesicles in presynaptic membrane
Purpose of the refractory period
So that impulse can only travel in one direction
