week 2 Flashcards
Describe the anatomical and functional divisions of the nervous system
The nervous system is broken up into 2, CNS and PNS,
CNS consists of the brain and spinal cord, PNS consists consists of everything else
1: sensory receptors ( detect position, touch, pressure pain, and temp, special senses)
2 -> sensory afferent division (brings information to CNS)
3 -> information processing (coordinates sensory input and motor functions)
4 -> motor (efferent division) PNS carries motor commands from the CNS to peripheral tissues and systems
- Somatic nervous system - voluntary
-automatic nervous system - involuntary (para and sympathetic division)
5 -> effectors - target organs and tissues that respond to neural motor commands
sketch and label the structure of a typical neuron and describe the functions of each component
dendrites: appears like a tree branch and is where neurons recieves input (neurotransmitters) from previous neuron
Axon: carries nerve impulses away from the cell body
Cell body: the region of the neuron containing the nucleus (metabolic centre of the neuron)
synapse with next neuron
axon terminal: where neurotransmitters are released into synaptic cleft for cell to cell communication
myelin sheath: insulating layer (fatty substances and proteins) allows electrical impulses to transmit quickly and efficiently along nerve cells
node of ranvier: gaps in the myelin sheath and serves to facilitate rapid conduction of nerve impulses.
Classify and describe neurons on the basis of their structure and function
anaxonic neurons:
functions are poorly understood, but they are located in the brain and special sense organs. They are small and lack anatomical features that distinguish dendrites from axons
Bipolar neurons:
the cell body is seperated from the dendrites by a long dendritic process. Cell body is followed by an axon.
Rare, but found in special senses and relay information about sight, smell, or hearing from receptor cells to other neuron. Smallest neuron.
Unipolar neuron:
dendrites and axon are continous, and cell body lies off to the one side. Most sensory neurons of the PNS are unipolar. Axon may extend a meter or more, the longest carries sensations from the tips of the toes to the spinal cord.
Multipolar neurons:
two or more dendrites and a single axon
most common neurons in the CNS
All motorneurons that control skeletial muslces
can be as long as unipolar neurons
describe the locations and functions of neuroglia in the CNS
glial cells are none -neuronal cells located in the CNS that do not produce electrical impulses.
Ependymal cells: produce CFS
microglia: resident immune cells of the brain and spinal cord
Astrocytes: peform metabolic, structural, homeostatic and neuroprotective tasks such as clearing excess neurotransmitters, stabalizing and regulating the BBB and promoting synapse formation
oligodendrocytes: myelinating cells of the CNS (they produce the myelin)
Describe the general role of the membrane potential changes in the neuronal activity
1: resting membrane potential: undisturbed cell, all neural activities begin with a changie in the resting membrane potential of a neuron,
2: a typical stimulus produces a temporary localised change in the resting membrane potental. This change, which decreases with distance away from the stimulus is called a graded potential.
3: if the graded potential is sufficiently large, it generates an action potential in the excitable membrane of the axon. An action potential is an electrical event that involves the location on the excitable membrane. One an action potential developes in one location, it spreads across the surface on an axon towards the axon terminals.
4: synptic activity then produces graded potentials in the plasma membrane of the postsynaptic cell, releasing neurotransmitters. These compounds bind to receptors on th postsynaptic plasma membrane changing its permeability.
5: the response of the postsynaptic cell depends on the degree of activity by the stimulated receptors.
explain how the resting membrane potential is created and maintained
resting membrane potential is an unstimulated or undisturbed cell
RMP of neurons is -70 as the cytosol contains an abundance of negtively charged proteins.
Important to note that potassium and sodium are postivitely charged ions they can diffuse into the cell through sodium or potassium leak channels
THe RMP is further maintained by the sodium-potassium pump
describe the functions of gated channels with respect to the permeability of the plasma membrane
3 different types of gated ion channels within the plasma membrane that open or close in response to specific stimuli
chemically gated:
open when they bind specific chemicals. The receptors that bind ACh are chemically gated, as they allow sodium to enter. Most abundant on dendrites and cell body (this is where the most synaptic communication occurs),
Voltage gated ion channels:
they open or close in response to changes in the membrane potential. Most common in neurons are Na, Ca, and K channels,
mechanically gated ion channels:
open in response to mechanical stimuli tht physically distort the neurons membrane surface. Important for sensory receptors for stretch, pressure, or vibration.
describe graded potentials
also known as local potentials: are changes in the membrane potential that cannot psread far from the site of stimulation. any stimulus that opens a gated ion channel will produce a graded potential
Describe the events involved in the generation and proagation of an action potential
generation of an action potential is a result of sodium ions rush back into the cell, their positive charge changes the potential inside the cell from negative to more positive. If a threshold potential is reached, then an action potential is produced.
depolarization to threshold: a graded depolarization brings an area of excitable membrane to threshold (-60mv)
Activation of sodium channels and rapid depolarization: voltage gated channels open and sodium ions move into the cell. The mmbrane potential rises to 30+ mv
Inactivation of sodium channels and activation of potassium channels: sodium channels close, voltage gated potassium channels open, k out of cell, repolarisation begins.
Potassium channels close: the voltage gated k channels begin closing. Near threshold the voltage gated sodium channels reactivates and the membrane soon returns to normal resting state.
propgation refers to the action potential moving along the cell membrane of an axon until it reaches the terminal button.
abslolute refactory perioid - cell cannot depolarise
relative refactory period - cell can depolarise but needs a larger stimulus
describe the generation structure of synapses in the CNS and PNS and discuss the events that occur at a chemical synapse
Chemical synapses rely on neurotransmitter release (most common synapse of neurons)
there are many neurotransmitters, focus on ACh
Step 1: the normal stimulus for neurotransmitter release is the depolarization if the axon terminal by the arrival of an action potential
step 2: The depolarization of the axon terminal opens voltage-gated calcium on channels, Calcium ions rush into the axon terminal and trigger exocytosis of the synaptic cesciles and the release of ACh into the synpatic cleft, The claciul ions that triggrred exocystosis are rapidly removed, ending the release of ACh.
step 3: THe released ACH diffuses across the sunaptic cleft and binds to chemically gated na receptors on the postynaptic membrane. The greated the amount of ACh released, the more receptors respond, thus the lartger the depolarization, If the depolarization is great enough to reach threshold, then an action potential will be generated in the postsynaptic neurons membrane.
step 4: The effects of on the postsynaptic membrane are temporary becaus of AChe, an enzyme within the synaptic cleft that break down ach. Other ach molecules diffuse away from the sunaptic cleft,
discuss the significane of postsynaptic potentials, including the roles of excitatory postsynaptic potentials and inhibitory postsynaptic potentials
post-synaptic potentials are graded potentials that develop in the postsynaptic membrane in response to a neurotransmitter. 2 major are excitatory and inhibitory
EPSP graded depolarization caused by the arrival of a neurotransmitter to the postsynaptic membrane that shifts the potential closer to the threshold, therefore needs a lower stimulus to activate an action potential
glutamate: sodium and calcium enters the cell
IPSP graded hyperpolarisation of the postsynaptic membrane, therefore a larger stimulus is required for an action potential.
Gaba: chloride enters the cell
