Nervous system Flashcards
What is the interstitial space
the space around the cells
the nervous system
is the bodys electrical communications network
generates and transmits information throughout the body in the form of electrical impulses
CNS and PNS
CNS - brain and spinal cord
PNS - nerves leaving the CNS
Central Nervous System
works as control centre
receives information
processes it and sends out instructions
info from receptor cell is transmitted by nerve impulses to the brain
Peripheal nervous sytem
whole body is supplied by it
given off as cranial nerves from the brain and spinal nerves from the spinal cord
Functions of CNS, PNS
- sensory input - nerve cells called sensory neurons collect info and transmit impulse
integration - the CNS processes the input
Motor output :
in response, the PNS sends out impulses through motor nerves to muscles, glands and other organs
PNS
Cranial nerves
spinal Nerves
Autonomic nerves - supply smooth muscle, cardiac muscle and glands and are under involuntary control. 3 sub divisions
- sympathetic ‘fight or flight’
-parasympathetic
- enteric
Somatic nerves - supply the skeletal muscle and are under voluntary control
The nervous system
central NS - body’s master control unity (Spinal Cord, Brain Stem, Brain)
Peripheral NS - the body’s link to the outside world ( The autonomic NS, The somatic NS, Sympathetic NS, parasympathetic, NS
Nervous tissue
- Neurons - responsible for transmission of nerve impulses from one neuron to another via a synapse
- Neuroglial cells - connective tissue supports the neuron (structurally, by offering essential nutrients, by creating myelin sheaths, by destroying pathogens)
what is a Schwann cell
its a neuroglial cell
Node of ranvier
between the schwann cells
dendrites and cell body
cell body - contains the nucleus, mitochondria and organelles
Dendrites - are extensions that branch from one end of the cell body. They recieve information from other neurons and send impulses towards the cell body
Axon
the axon is a cable like projection located on the opposite end of the cell body from the dendrite. The axon carries the impulses away from the cell body and towards the next neuron in the chain
Nerve endings / Axon terminals
neuron may connect to
- another neuron (synapse)
- or to a muscle (neuromuscular junction )
Neurons can be myelinated or non myelinated
Myelin is a fatty substance that is produced by schwann cells and forms a sheath round myelinated neurons
Nodes of Ranvier
gaps in between areas of myleination are called nodes of ranvier
the transmission of nerve impulses is more rapid in a myelinated neuron as the impulses jump from node to node
3 types of neuron
- sensory
- motor
- interneurons
Sensory Neurons (afferent)
afferent means ( moving towards)
these neurons respond to sensory stimuli detected by the sensory receptor endings
they pass the impulses towards the spinal cord and brain CNS
Motor Neurons ( efferent)
Efferent means moving away
transmits impulses from the brain and spinal cord to effector organs and triggering responses from these organs (muscle contraction or release of the glands product)
Interneurons or intercalated neuron
also called association or relay neurons
connect neurons to other neurons
lie between a sensory and motor neuron
Neuroglial cells
support neurons in several ways, including physically holding them in place and supplying them with nutrients
protect neurons from pathogens and remove dead neurons
certain types of glial cells produce myelin
A Nerve
a nerve is a bundle of neurons
An individual axon plus its myelin sheath is called a nerve fibre
Nerves provide a common pathway for the electrochemical nerve impulses
Nerve fibres can be of three types
Motor - which send impulses away from the CNS
Sensory - which send impulses towards the CNS
Mixed - carry both sensory and, motor fibres
Visceral sensory and motor nerves
associated with organs and body systems - involuntary control
Somatic sensory and motor nerves
Associated with the somatic structures (muscles, joints, tendons). Voluntary control
Nerve impulse conduction
at the end of the neuron there is a gap before the next cell
if the next cell is another neuron, the gap is known as a synapse
if the next cell is a muscle cell, the gap is known as a neuromuscular junction
the neuron before the synapse is known as the presynaptic neuron, the neuron after the synapse is postsynaptic
Neurotransmitters
Travel between neurons at the synaptic cleft (gap between neurons)
- Acetylcholine
- Adrenaline
- dopamine
- serotonin
Impulse conduction simplified
- calcium - gated channels open
- calcium ions enter the synaptic terminal and cause the release of a chemical called a neurotransmitter
- the neurotransmitter diffuses across the synapse to the next cell
- this stimulates sodium channels to open in the postsynaptic membrane
nerve impulses
nerve impulses are electrical in nature
depolarisation - generation of electrical impulse
repolarisation - recharging
Nerve impulses are an ‘ all or nothing’ phenomenon. The nerve is either stimulated (depolarised) or not
Nerve impulses (polarised)
NB - electrolytes carry a charge
we could refer to this state as polarised - meaning big difference
depolarization of a neuron
- sodium channel opens on neuron cell membrane
- sodium ions flow into cell by passive diffusion
- increase in sodium leads to a positive electrical charfe
repolarization of a neuron
- sodium channels close
- k+ channels open
- k+ diffuses out of the cell
- resting state restored
as repolarization ends, sodium - potassium pump moves sodium and potassium ions back to their original sides
Cranial nerves
12 pairs of cranial nerves that emerge directly from the brain and brain stem
cranial nerves are referred to in roman numerals
exit the skull via foramen
each pair is dedicated to particular functions
Cranial Nerves
some have a sensory fucntion -
bring info from the sense organs to the brain
others have a motor function -
control muscle, tissue and organ activity
some have mixed sensory and motor functions
