Nervous System Flashcards
What is a neuron?
Specialised cell with cell bodies containing a nucleus and long extentions or fibers that transmit signals.
Basic parts of the neuron
A cell body and cell extensions called dendrites and axons
What is the cell body
The region of the neuron around the nucleus that is responsible for producing substances that are necessary for the nerve cell to live and carry out its functions
What is an axon?
A single long cell extension that often makes distant connections.
May give out branches which often split off and right angles and usually have a myelin covering.
What are nerves?
Bundles of neurons that give off message signals called nerve impulses
What is a dendrite?
A cell extension that is usually much smaller than an axon, has no myelin covering and is specialised to recieve impulses from sensory cells or from axons of other neurons.
What is the CNS
Central Nervous System - consisting of brain and spinal cord
What is PNS
Peripheral Nervous System - consisting of nerves that run to and from the CNS
Note on - Sensory Neurons
Receive information froma sensory receptor (special structures that detect changes in the environment).
Most have one long axon bringing messages from particular receptors
Cell bodies lie near the CNS
Note on - Interneurons
Located within the CNS - integrate incoming information with out going messages.
Usually have a highly branched system of dendrites able to receieve input from many different neurons at once
Axons may not be myelinated.
Note on - Motor Neurons
Transmit commands away from central nervous system to the muscles and glands.
One long axon, usually branched at the end, bringing messages to a muscle or gland
What are Neuroglial cells and what are CNS glial cells and PNS glial cells
-Companion cells that provide support, protectionand nutritional stability to the neuron.
-CNS glial cells - Microglia, Ependymal cells, Astrocytes, Oligodendrocytes
-PNS glial cells - Satellite cells, Schwann cells
Function of Microglia
- monitor health and perform defence functions for neurons.
-differentiate to become a type of macrophage to phagocytose debris and microorganisms
Function of Ependymal cells
-line the central cavities of the brain and spinal cord and help circulate cerebrospinal fluid.
Function of Astrocytes
-regulate the chemical environment around the neurons and exchanges between neurons and capillaries
Function of Oligodendrocytes
Wrap around neuron fibres, forming myelin sheath
Function of Satellite Cells
Multifunctional especially during disease.
Found surronding neuron cell bodies within ganglia
Function of Schwann Cells
Found wrapped around and insulating axons of sensory and motor neurons forming a myelin sheath.
What are the Nodes of Ranvier?
Uninsulated spots that occur at regular intervals on an axon.
-These nodes and mylein sheath create conditions that speed the nerve impulses as it is conducted along surface of axon
Functions of neurons:
To transmit info:
-From the environment to the spinal cord and brain
-From one cell to another within the CNS
-From brain and spinal cord to other parts of the body
Nerve cells transmit this infor in form of nerve impulses
When at rest, what is the charge of the cytoplasm and why?
Approx -65 millivolts
Means that the insde of the cell is negatively charged (greater conc of K+ inside axon) relative to extracellular fluid along the outside of the membrane (greater conc of Na+ outside an axon)
Which ions play a principle role in the development of electrical potential along the membrane of the neuron?
Sodium (Na+) and Potassium ions (K+)
Transmembrane protein embedded within cell membranes of neurons
Sodium-potassium pumps - uses the energy stored in molecules of ATP (active transport) to move K+ into the neuron at the same time as they move Na+ out of the neuron - maintain resting potential
What is a stimulus
An internal or external environmental change taht excites a neuron
What is an action potential?
A rapid change in polarity across the membrane of the neuron
-If the stimulus causes the axomembrane to depolarise to a certain level an action potential occurs.
What happens at the 2 types of gated channel proteins required by the action potential
1) Sodium gates open : Na+ flows into cell. Membrane potential changes from -65mV to +40mV - depolarisation
2) Potassium gates open : K+ flows to outside axon. Membrane potenmt
What is the purpose of a refractory period
It prevents the action potential from going backwards as the Na+ gates are unable to open
What does the myelin sheath do?
It acts as an insulator. It prevents the transport of ions across the neuron membrane beneath it
Where can the action potential be generated?
Only at the nodes of Ranvier where the gated channels are concentrated
What is saltatory conduction?
A very fast form of nerve impulse conduction where the action potential jumps from one node to the next causing depolarisation only at these specific points
What are effectors?
Muscles & glands - response occured when stimulated by nerves
What is a synapse?
Where a neuron communicates with another neuron or an effector
What is the synaptic cleft?
Minute gaps separate neurons and effectors at synapses
How many neurotransmitters are there?
25
What removes neurotransmitters from the synaptic cleft?
Enzymes
What neurotransmitter is found at the neuromuscular junction?
Acetylcholine
What enzyme works on acetylcholine
Acetylcholinesterase - broken down to acetic acid & choline
What is membrane on the axon side of the synapse?
Presynaptic membrane
How do neurotransmitters work?
Depolarisation reaches the presynaptic membrane - calcium rushes in - sudden rise in cytoplasmic Ca causes the release of neurotransmitters into synaptic vesicles - merge with membrane and released into the cleft - diffuse to the other side of the cleft - bind with receptor molecules in postsynaptic membrane and cause the opening of ion channels
What is an excitatory synapse?
Neurotransmitters depolarised postsynaptic membrane - continuation of nerve impulse
What is an inhibitory synapse?
Reduces the ability of the postsynaptic membrane to depolarise
What is grey matter?
contains cell bodies and short
nonmyelinated nerve fibres
What is white matter?
myelinated fibres that run in
bundles called tracts
What is the somatic nervous system?
motor neurons that control voluntary responses
What is the autonomic nervous system?
Motor neurons that carry messages about involuntary activities
What are the parts of the brain?
The cerebrum, thalamus,
hypothalamus, cerebellum, and brain stem.
What is the cerebrum?
-receives sensory information
-sends messages to move skeletal muscles
-integrates incoming and outgoing nerve impulses
-performs activities such as thinking, learning, & memory
What is the thalamus?
Relays most sensory information from the spinal cord and
central parts of the brain to the cerebral cortex.
➢ Interprets certain sensory messages such as those of pain,
temperature, and pressure.
What is the hypothalamus?
➢ Controls various homeostatic functions such as body
temperature, respiration, and heartbeat.
➢ Directs hormone secretions of the pituitary gland
What is the cerebellum?
Coordinates subconscious movements
➢ Contributes to muscle tone, posture, and balance
What is the brain stem?
-origin of many cranial nerves
-reflex centre for movements of eyeballs, head, and trunk
-regulates heartbeat and breathing
-plays a role in consciousness
-transmits impulses between brain and spinal cord.
What is the spinal cord?
Extends from the brain stem down the back through the vertebral column
Tiny central canal filled with cerebrospinal fluid continuous with fluid-filled sacs in brain
fluid acts as a shock absorber, and brings nutrients, hormones and wbc to parts of the brain
What are the 3 parts of the autonomic nervous system?
Sympathetic, parasympathetic, and enteric
What does the enteric nervous system control?
Digestion system
What does the parasympathetic control?
The ‘rest & digest’ response
