8. nervous system Flashcards
Explain the functions of the nervous system
- receive sensory input
- integrate information
- Controlling muscles and glands
- Maintaining homeostasis
- Establish and maintain mental activity
divisions of the nervous system
- nervous system
- peripheral nervous system and central nervous system
- somatic, autonomic, enteric nervous system
- from each of the three there is motor (efferent) and sensory (afferent)
- comes from the motor of the autonomic nervous system sympathetic and parasympathetic
- Central nervous system
decision maker of the body
Brain and spinal cord
Peripheral nervous system
messengers sendings messages to brain and spinal cord
sensory receptors
Cranial nerves: 12 pairs
Spinal nerves: 31 pairs
Ganglia: collection of neuron cell bodies outside of CNS
Plexuses: extensive network of axons outside CNS
Somatic nervous system
voluntary
From the CNS to skeletal muscles
Skeletal muscle contracts
Single neuron, one synapse
Autonomic nervous system
involuntary
From the CNS to smooth or cardiac muscle or glands
Two neuron, two synapses
Enteric nervous system
nerve plexuses within the wall of the digestive tract
Sensory neurons connect digestive tract to CNS
Sensory division
Afferent
Collects input from specialised receptors
Transmits the input as electrical signals to CNS
Motor division
Efferent
Transmits electric signals form CNS to effector (muscles, glands)
Sympathetic
fight or flight response
Primes the body to act in threatening situations
Quicker response
Eg increased heart rate, sweating
Parasympathetic
rest and digest response
Relaxes the body inhibiting high energy functions
Slower response
Eg stimulates digestion
Differentiate between the somatic and autonomic nervous systems.
- Somatic nervous system
voluntary
From the CNS to skeletal muscles
Skeletal muscle contracts
Single neuron, one synapse - Autonomic nervous system
involuntary
From the CNS to smooth or cardiac muscle or glands
Two neuron, two synapses
Contrast the general functions of the CNS and PNS.
- Central nervous system
decision maker of the body
Brain and spinal cord - Peripheral nervous system
messengers sendings messages to brain and spinal cord
sensory receptors
Cranial nerves: 12 pairs
Spinal nerves: 31 pairs
Ganglia: collection of neuron cell bodies outside of CNS
Plexuses: extensive network of axons outside CNS
structure of neurons
Neuron - receive information, integrate it and send appropriate response to target
3 main parts
1. Neuron cell body (soma)
2. Dendrites
3. Axon
Neuron cell body (soma)
nucleus, nasal bodies, Golgi apparatus, mitochondria
Dendrites
highly branched extensions of cell body
Conduct impulses from other axons or nerve cell bodies towards the cell body
Flow of current from tip of dendrites to cell body
Axon
vary in length
Conducts nerve impulses away from the cell body to the presynaptic terminals
The axon branches out into axon terminals, at the end of these terminals are knobs called synaptic knobs
Synaptic knobs: axon endings
Myelin sheath: schwan cells around axon
Node of ranvier: area in between the schwan cells
Multipolar
Several dendrites and one axon
Bipolar
One dendrite and one axon
Retina or eye, nasal cavity
Unipolar
One axon split into 2
Sensory neuron
conduct action potential from sensory receptors to CNS
Afferent neuron
Axons found in CNS
cell bodies are outside the CNS in dorsal root ganglion
Motor neuron
conduct action potation away from CNS towards muscles or glands
Efferent neuron
Axon in muscle or gland
Cell bodies in the CNS
Interneuron
conduct action potential within CNS from one neuron to another
neuroglial cells in the CNS and PNS
CNS
- Microglial cells
- Oligodendrocytes
- Astrocytes
PNS
- Schwann cells
- Satellite cells
Microglial cells
in CNS
immune cells
Become active, mobile and phagocytic in response to inflammation
Phagocytose foreign substances, necrotic tissue, pathogens
Oligodendrocytes
in CNS
have cytoplasmic extensions that wrap around axon forming myelin sheath
Each cell can enclose multiple axons
Astrocytes
in CNS
highly branched cytoplasmic processes with end feet
Scaffold CNS cells and capillaries, control blood brain barrier permeability, form glial scar during injury, synaptic support
Form scar tissue around injury to promote recovery and prevent further injury
Schwann cells
in PNS
have cytoplasmic extensions that wrap around axon forming myelin sheath
Insulation of axons, saltatory conduction of action potential
1 schwann cell = 1 axon
Satellite cells
in PNS
surround neuron cell bodies in sensory and autonomic ganglia
Provide support and nutrition to cell bodies
Protects neurons from heavy metal poisons
resting membrane potential
the difference in charge across the cell membrane in a resting cell
- RMP caused by leak ion channels and the Na+/K+ pump
1. Resting membrane potential
2. Depolarisation
3. Repolarisation
4. End of repolarisation and the after potential
5. Resting membrane potential
- Resting membrane potential
all gates Na+ and K+ channels are closed
K+ leak channels are open which allow movement of K+ outside of the cell
= negative intracellular charge, positive extracellular charge
- Depolarisation
Na+ voltage gated channels open and Na+ moves into the cell and inside of the cell becomes more positive
K+ channels are closed
Membrane potential becomes more positive
Creates an action potential = moving the depolarisation along the membrane from one location to the next
- Repolarisation
Na+ channels close
K+ channels open and K+ moves out of the cell
Membrane potential becomes more negative and outside the cell becomes positive
Wants to go back to its original membrane potential
- End of repolarisation and the after potential
Na+ channels close
K+ channels close slower so K+ continues to leave the cell and this produces the after potential
Membrane potential becomes very negative
- Resting membrane potential
Na+ and K+ channels are closed
Resting membrane potential is re-established by Na+/K+ pump which redistributes ions as all Na+ and K+ channels are closed
All or none concept
magnitude will stay the same or if the threshold isn’t reached then there will be no action potential, no such thing as a smaller action potential
Refractory period
another action potential cannot be generated at this time
Describe the characteristics of stimulating a neuron.
- a neuron that is stimulated causes voltage gated Na+ channels to open and Na+ moves into the cell, the voltage gated K+ channels remain closed
Describe the effect of myelination on the speed of action potential conduction.
Schwann cells wrap themselves around the axon and cover it with myelin
At the end of the schwann cells is a segment no covered by the sheath = node of ranvier
Saltatory conduction occurs in all myelinated axons
Resting membrane potential is changed at the exposed nodes of ranvier
The impulse jumps between the nodes increasing the speed of conduction
synapse
junction of a neuron with another cell
Electrical synapse
less common, electric signal, only in cardiac and some smooth muscles
Chemical synapse
most common, uses chemical messenger, a neurotransmitter to transmit AP across synapse
Components of synapse
pre synaptic terminal
Pre synaptic membrane
Post synaptic membrane
Synaptic cleft
Neurotransmitters
Synaptic vesicles
Events that occur at synapse
Action potential arrives at pre-synaptic terminal
Calcium channels open and calcium ions diffuse into the cell and act on vesicles
Vesicles (containing neurotransmitters) move to the presynaptic membrane
Neurotransmitters are released into the synaptic cleft via exocytosis
Neurotransmitters cross the synaptic cleft
Neurotransmitters bind to receptors of ion channels on the post synaptic membrane
Ion channels open allowing diffusion of ions into the post synaptic cell
Neurotransmitters removed from synapse by enzyme activity
Neurotransmitter release
Action potentials arriving at the presynaptic terminal cause gated Ca2+ channels to open
Ca2+ diffused into the cell and stimulates exocytosis of the synaptic vesicles which releases neurotransmitter molecules
Neurotransmitter molecules diffuse from the presynaptic terminal across the synaptic cleft
Neurotransmitter molecules combine with their receptor sites and cause ligand gated Na+ channels to open. Na+ diffuses into the cell and causes depolarisation
Neurotransmitter removal
Acetylcholine molecules bind to their receptors
Acetylcholine molecules unbind from their receptors
Acetylcholinesterase splits acetylcholine into choline and acetic acid which prevents acetylcholine from binding to its receptors. Choline is taken up by the presynaptic terminal
Choline is used to make new acetylcholine molecules that are packaged into synaptic vesicles
Other acetylcholine molecules simply diffuse into the extracellular fluid away from the synaptic cleft
Reflex
automatic response to stimulus without the higher brain involvement
rapid, predictable and unlearnt
Eg spoon on knee
Somatic or autonomic
Types of reflexes
somatic : involves skeletal muscles
Autonomic: involves smooth or cardiac muscles or body organs
Eg shining light into the eyes, the pupils adjust
Monosynaptic: simple neuronal pathway, sensory synapses with motor neuron, one synapse
Polysynaptic: complex pathway, multiple synapse with interneurons eg knee jerk reflex
Reaction
voluntary response to the stimulus
slower then a reflex as it has to travel to the brain before the reaction occurs
Reaction time improves through repetition
Eg catching a ball, dodging an incoming object
Cranial nerves:
12 pairs
Spinal nerves
31 pairs
Ganglia
collection of neuron cell bodies outside of CNS
Plexuses
extensive network of axons outside CNS
Neuron (nerve cell)
basic structural and functional unit of the nervous system
Neuroglia
major supporting cells of neurons
Axon
nerve fibre
Nerve
bundle of axons and their sheaths
Sensory receptors
seperate specialised cells which detect temperature, pain, touch, pressure, light, sound
Action potentials
electrical signal
Effector organ or effect cell
the organ, tissue or cell in which an effect or an action takes place
Membrane potential
measure of electrical properties of cell membrane
Grey matter
consists of neuronal cell bodies, dendrites, axon terminals, ganglia, unmyelinated axons
- in middle of spinal cord
White matter
few cell bodies,
white due to myelin sheath
Lies on inner side in brain but on periphery in spinal cord
