Week 11 - How do we control ourselves? Flashcards
What are the functions of the nervous system?
- maintaining homeostasis
- receives sensory input (internal and external)
- integrating information
- motor output
- establishing and maintaining mental activity
What are the two structural divisions of the nervous system?
central nervous system - brain and spinal cord
peripheral nervous system - spinal nerves and cranial nerves
What are sensory receptors?
separate specialised cells which detect temperature, pain, touch, pressure, light, sound, odour and stimuli
What is a nerve?
bundle of axons (nerve fibres) and their sheaths
What is a ganglion?
collection of cell bodies located outside the CNS
What is a plexus?
extensive network of axons or cell bodies
What is a synapse?
a junction of a neuron with another cell
Autonomic division
- involuntary, subconscious
- CNS to smooth muscle, cardiac muscle or glands
- two neurons
- cell bodies of neurons located in the CNS and autonomic ganglion
Somatic division
- voluntary, conscious
- CNS to skeletal muscle
- single neuron
- cell bodies located in CNS
What is neuron?
structural unit of the nervous system
Describe the functional types of neurons
- sensory (afferent) - body -> CNS
- motor (efferent) - CNS -> body
- inter neuron - from one neuron to another
Describe the structural types of neurons
- multipolar- many dendrites, single axon
- bipolar - axon, dendrites
- unipolar - one axon away from cell body
What are the types of neuroglia found in the CNS and PNS?
CNS: astrocytes, ependymal cells, microglia, oligodendroxytes
PNS: schwann cells, satellite cells
Astrocytes
- CNS
- supporting framework for blood vessels and neurons
- assist in the formation of tight junctions between endothelial cells of capillaries
- blood-brain barrier
- respond to tissue damage in CNS
Ependymal cells
- CNS
- line central cavities of brain and spinal cord
- assist in movement of CSF
Microglial cells
- CNS
- monitor health of surrounding neurons using extensions
- phagocytose microorganism, infection trauma or inflammation
Oligodendrocytes
- CNS
- cover axons which forms an insulting sheath around them –> myelin sheath
Schwann cells
- PNS
- forms a myelin sheath around axons –> insulating
Satellite cells
- PNS
- provide support and nutrition to cell bodies in ganglia
- protect cell bodies from harmful substances
Where is grey matter found in the CNS?
Brain: outer cortex (superficial) and nuclei (deeper)
Spinal cord: inner ‘grey’ part
Where is grey matter found in the PNS?
ganglion
Where is white matter found in the CNS?
Brain: deeper nerve tracts
Spinal cord: outer part
Where is white matter found in the PNS?
nerves
What does grey matter consist of?
cell bodies and dendrites
What does white matter consist of?
axons
What causes membrane potentials to be generated?
- differences in ionic concentrations (sodium and potassium)
- permeability of cell to ions (movement of ions)
Non-gated ion channels
- ‘leak’ ion channels
- cell membrane has more potassium leak ion channels open compared to sodium leak ion channels
Gated ion channels
- require signals to open
- ligand-gated = chemically gated
- voltage-gated = change in charge
- other-gated ion channel = touch, temp, pressure et
How do ions move in and out of cells?
gated and non gated ion channels
What is resting membrane potential?
difference in charge across cell membrane ina resting cell
- intracellular side more negative
- -70mV
- caused by leak ion channels and sodium/potassium pump
- more potassium outside contributing to negative charge
What is depolarisation?
membrane potential becomes more positive (inside of cell becomes more positive)
What is hyperpolarisation?
membrane potential becomes more negative (inside of cell becomes more negative)
What is repolarisation?
membrane potential returns to normal
Graded potential
- CAN lead to an action potential
- short-lived, localised changes in membrane potential
- often occurs in dendrites
- ability to summate
What occurs at resting membrane potential with gates?
- all gated sodium and potassium gates are closed
- potassium leak channels open (potassium to outside of cell) –> negative intracellular charge)
- sodium/potassium pump also works to maintain RMP
What occurs at depolarisation with gates?
- sodium gated channels open and sodium moves into cell (more positive inside)
- potassium gated channels closed
What occurs at repolarisation with the gates?
- sodium gated channels close
- potassium gated channels open and potassium moves out of the cell (slightly negative inside)
What occurs at hyperpolarisation?
- sodium channels close
- potassium channels close slowly so potassium continues to leave the cell
What happens again at resting membrane potential?
- sodium and potassium gated channels close
- resting potential re-established by sodium/potassium pump which redistributes ions
All-or-none principle
action potential happens completely or not at all
Refractory period
- absolute: beginning to end of transmission to ensure no interruptions
- relative: cannot respond to another stimulus following absolute refractory period
Saltatory conduction
along myelinated fibres
What are the two types of synapses?
- electrical
- chemical synapses
What is the process of transmission across a chemical synapse?
- action potential arrives at terminal
- causes voltage-gated calcium ion gates to open
- calcium floods into the presynpatic terminal
- calcium causes vesicles closer to membrane
- vesicles fuse to membrane and release neurotransmitters into synapse
- neurotransmitters diffuse across and bind to sodium gated channels (ligand-gated_
- gates open and sodium moves into the cell
- change in charge = graded potential
How are neurotransmitters removed?
- breakdown by enzymes
- re-absorption into presynaptic terminal
- diffuse away from synapse
Why must neurotransmitters be removed from the cell?
muscles (or other effector) will continue to contract continuously
What is a reflex?
- automatic response to a stimulus
- can be somatic or autonomic
What is the simplest reflex arc?
do not involve interneurons (eg mono-synaptic)
What are the components of a typical reflex arc?
- sensory receptor
- sensory neuron
- interneuron
- motor neuron
- effector organ
What is the purpose of the stretch receptor of the patella tendon?
stablises leg when standing, monosynaptic
