how nerves work Flashcards
describe anatomical organisation of nervous system
nervous system divided into 2 parts = CNS & PNS
PNS can be divided into sensory and efferent, sensory sends info to CNS through afferent neurons and efferent takes info from CNS to target cells via efferent neurons
efferent neurons can be divided into autonomic and somatic - autonomic further into sympathetic and parasympathetic
general structure of neurone
neurons consist of a cell body, with a nucleus, and which has processes - dendrites or axons - which receive incoming signals, or carry outgoing info , respectively. axons and dendrites are essential for neuronal communication.
axons are wrapped in a myelin sheath.
ionic basis of resting membrane potential
determined primarily by K+ conc gradient and cell’s resting permeability to K+, Na+, and Cl-, change in K+ conc gradient or ion permeabilities changes membrane potential
cell membrane of neuron only slightly permeable to Na+
if membrane suddenly increase Na+ permeability, Na+ enters cell, moving down electrochemical gradient
addition of positive Na+ to ICF DEPOLARIZES the cell membrane and creates and electrical signal
membrane can also be HYPERPOLARIZED - addition of K+ , positive charge is lost from inside cell and cell becomes more negative , may also hyperpolarize if Cl- enter cell from ECF
properties and functions of graded potentials
variable-strength signals that travel over short distances and lose strength as they travel through cell
used for short distance communication
if depolarising potential is strong enough when it reaches an integrating region within a neuron, initiates an action potential
ionic basis of action potential
large depolarisations that travel for long distances through a neuron without losing strength function is rapid signaling over long distances ie toe to brain Na+ and K+ are both involved , voltage-gated channels
classification of nerve fibre types
myelinated:
group A
group B
group C - unmyelinated
define conduction velocities
measures how fast an electrical impulse moves through nerve
conduction velocities and relationship with fibre types
group A -
group B - slow
group C - slow
consequences of demyelinating disease
vision loss muscle weakness muscle stiffness spasms loss of coordination change in sensation pain changes in bladder and bowel function
structure of neuromuscular junction
presynaptic part (nerve terminal) postsynaptic part (motor endplate) synaptic cleft = area between nerve terminal and motor endplate
describe process of neuromuscular transmission
describe ultrastructure and functions of synapses between neurones
permits neurons to pass an electrical or chemical signal to another neuron or to the target effector cell
synapses are essential to transmission of nervous impulses from one neuron to another
excitatory = found mainly on dendrites and dendritic spines inhibitory = concentrate on cell soma and axonal initial segment, with sparse distribution along both spiny and nonspiny dendritic shafts
describe processes of synaptic transmission in CNS
explain role of synapses in integration of neuronal function
when presynaptic neuron emits a spike, then neurotransmitters are released from the synapses and bind to receptors located in the postsynaptic cell to excite or inhibit the postsynaptic neurons
connect neurons in brain to neurons in rest of the body and from those neurons to the muscle
common excitatory neurotransmitters
acetylcholine noradrenaline glutamate histamine dopamine
common inhibitory neurotransmitters
serotonin
gamma-aminobutyric acid (GABA)
glycine
explain basic properties of signal transduction in neurones
binding of ligand results in a conformational change in receptor - this change in shape triggers events within the cell
receptor activates an effector eg enzyme
explain term EPSP
excitatory postsynaptic potential - depolarises cell and increases likelihood of initiating an AP
explain term IPSP
inhibitory postsynaptic potential - decrease likelihood of postsynaptic AP , can hyperpolarize or depolarize
structure and function of glia
function = communicate with neurons, also provide biochemical and structural support
saltatory conduction
temporal and spatial summation
Nernst equation
describes membrane potential that results if membrane were permeable to only 1 ion
acetylcholinesterase
cholinergic enzyme , found at postsynaptic neuromuscular junctions, especially in muscles and nerves
immediately breaks down or hydrolyses acetylcholine - naturally occurring neurotransmitter, into acetic acid and choline
difference between a nerve and neuron
nerve = bundle of neurons along with connective tissue sheaths, blood vessels and lymphatics neuron = cell of nervous system that conducts nerve impulses
what are nerves
long axons of both afferent and efferent peripheral neurons bundled together with connective tissue into cordlike fibres = nerves
only afferent signals = SENSORY
only efferent signals = MOTOR
both signals = MIXED
types of gated ion channels
mechanically
chemically
voltage-gated
mechanically gated ion channels
found in sensory neurons and open in response to physical forces such as pressure or stretch
chemically gated ion channels
in most neurons they respond to a variety of ligands, such as extracellular neurotransmitters and neuromodulators or intracellular signal molecules
voltage-gated ion channels
respond to changes in cell’s membrane potential
Na+ and K+ channels play important role in initiation and conduction of electrical signals along axon
group A nerve fibers
Aalpha - primary receptors of muscle spindle and golgi tendon organ,
Abeta - secondary receptors of muscle spindle and contribute to cutaneous mechanoreceptors, Agamma - motor neurons that control intrinsic activation of muscle spindle and
Adelta - free nerve endings that conduct painful stimuli related to pressure and temp
group B nerve fibers
myelinated
small diameter
low conduction velocity
primary role - transmit autonomic information
group C nerve fibers
unmyelinated
small diameter
low conduction velocity
lack of myelination = primary cause of slow conduction velocity
polymodal
schwann cells and oligodendrocytes
