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
