Lecture 16-26 Flashcards
2 parts which the nervous system is divided into:
Central nervous system (CNS) & Peripheral nervous system (PNS)
What does the CNS consist of?
The brain and spinal cord (made of neurons & glia)
What does the PNS consist of?
Peripheral nerves (made of neurons & glia)
In the CNS, a nucleus is..?
A group of cell bodies
In the CNS, a tract is…?
bundle of axons
What is grey matter?
Cell body groups, in the CNS
What is white matter..?
A bundle of axons, in the CNS.
In the PNS, what is the name for a group of cell bodies?
Ganglion
In the PNS, what is the name from axon bundles?
Nerve
What structures make up a neuron?
Dendrites, cell body, axon hillock, axon and axon terminals.
What sections of a neuron are found in the input zone? And what are their functions?
- Dendrites - receive a signal & sends the input to the cell body.
- Cell body - Receives & sums chemical signals, contains nucleus & organelles
What sections of a neuron are found in the summation zone? And what are their functions?
Axon hillock - This is where signals are integrated and a decision is made on wether to pass the signal or not.
What structures of a neuron are found in the conduction zone? and what are their functions?
Axon (can either be myelinated or un-myelinated) - This structure carries electrical signals between brain areas, to and from the spinal cord. From peripheral sensory receptors and to effector cells.
What structure(s) of a neuron are found int eh output zone? and what are their functions?
Axon terminals - they contact other neurons/effectors releasing neurotransmitter.
What are the 4 key types of neurons?
- Multipolar - multiple processes from the cell body
- Bipolar - 2 process from the cell body
- Unipolar - 1 process from the cell body
- Anaxonic - no distinct axon, all processes look the same.
What are the 5 types of glia (support) cells?
- Astrocytes
- Micro-glia
- Ependymal cells
- Oligodendrocytes
- Schwann cells
What is the functions of astrocytes?
To supply nutrients to neurons, ensheath blood capillaries & transmits information for injury response.
Function of micro-glia?
Immune cells that engulf micro-organisms and debris
Function of ependymal cells?
Line the fluid filled spaces un the brain & spinal cord to circulate cerebrospinal fluid (CSF) with their cilia.
Function of oligodendrocytes?
Support & myelinated neurons in the CNS
Function of Schwann cells
Supports & myelinated neurons in the PNS - similar to oligodendrocytes but are found in the PNS NOT the CNS
What is a synapse?
A connection between 2 neurons.
What does the synapse involve?
It involves the pre-synaptic neurons’ axon terminals and the post-synaptic neurons’ dendrites.
The nerve impulse is passed from neuron to neuron. And the signal goes;
Electrical —> Chemical —> Electrical
What is afferent information flow
Information that goes INTO the brain. Also known as ascending info
- Sensory information (incoming) which moves from;
the body -> peripheral nervous system (PNS) -> central nervous system (CNS)
What is efferent information flow
Information that goes OUT OF the brain. Also known as descending.
- Motor ‘instructions’ (outgoing) moving from;
central nervous system (CNS) -> spinal nerves -> effectors
What is the afferent/ascending process?
- Information enters the body through receptors
- Relay information to spinal nerves
- Relay to the CNS (spinal cord/brain)
What is the efferent/descending process?
- Motor output through motor neurons
2. Effectors respond to a motor command and produce and action.
What is somatic?
Voluntary or controlled.
- somatic efferent = (voluntary, outgoing info) -> e.g. running
- somatic afferent = (voluntary, incoming info) -> e.g. sight
What is autonomic?
Things you are unaware of, involuntary.
- Autonomic efferent = (involuntary, outgoing info) -> e.g. contraction of heart
- Autonomic afferent = (involuntary, incoming info) -> e.g. blood pressure.
What is the somatic efferent division?
This is the pathway in the body which allows for voluntary movement of our muscles, containing ONLY 2 NEURONS!
Neuron 1 is…?
The upper motor neuron:
- cell body in the brain and axon in the spinal cord.
- –> contained in the central nervous system (CNS) & myelinated.
Neuron 2 is…?
The lower motor neuron:
- cell body in the spinal cord and axon in spinal nerve to the effector (skeletal muscle at NMJ)
- —-> In the peripheral nervous system (PNS) & myelinated.
What is the neurotransmitter of the somatic efferent division?
Acetylcholine (ACh)
What is the Autonomic efferent nervous system?
This system allows for involuntary, outgoing information to get to the effector.
What are the two sub-divisions of the autonomic efferent nervous system?
Sympathetic & parasympathetic nervous systems
Neuron 1 - autonomic efferent nervous system
cell body in brain & axon in brain/spinal cord
Neuron 2 - autonomic efferent nervous sytem?
Cell body in the brain or spinal cord, with axons in the peripheral nervous system (PNS) synapsing in the autonomic ganglion.
NEUROTRANSMITTER = ACETYLCHOLINE (ACh)
Neuron 3 - autonomic efferent nervous system:
Cell body & axon in the peripheral nervous system (PNS) synapsing on the effector, unmyelinated.
NEUROTRANSMITTER = ACh or NOREPINEPHRONE
What is the sympathetic stress response?
‘fight or flight’ stress response.
- The neurotransmitter is noradrenaline
Results in an increased; heart rate, pupil size & sweating
And a decreased; gastric motility & salivation.
What is a parasympathetic stress response?
‘rest and digest’ stress response.
- The neurotransmitter is acetylcholine (ACH)
Is the opposite of the sympathetic response.
Where can the differences between the sympathetic and parasympathetic nervous system she found?
In the 2nd and 3rd neurons ONLY
Pre-ganglionic neuron - In the sympathetic nervous system…?
Cell body in thoracolumbar levels of the spinal cord.
Axons is short with the terminals in the sympathetic ganglion
Post-ganglionic neuron - In the sympathetic nervous system…?
Cell body in the sympathetic ganglion. \
Axon is long & unmyelinated
Pre-ganglionic neuron - In the parasympathetic nervous system…?
A.K.A - Neuron 2.
- Cell bodies are in the cranial & sacral levels
- Axon is long and terminates at the parasympathetic ganglia near the effector
Post-ganglionic nero - In the parasympathetic nervous system:
A.K.A - Neuron 3.
- Cell body in parasympathetic ganglia in/near the effector organs.
Axon is short.
What is resting membrane potential?
A difference in charge on the outside of the membrane compared to the inside
- The two ions important for the resting membrane potential (RMP) are NA+ and K+ & it is determined by their concentrations inside & outside the cells.
RMP = -70mV
What is a voltage-gated channel?
A type of channel that will ‘open’ when there is a change in voltage
- Will only occur when the local potentials are greater than the THRESHOLD POTENTIALS.
What is threshold potential?
The minimum potential needed ignorer for voltage-gated channels to open.
What are the 3 key channels that cause the propagation of Action potentials.
- Chemically gated channel (ligand-gated)
2. Mechanically gated channels.
Mechanically-gated channel…?
Activated / stimulated to open with pressure
Chemically-gated channel…?
Stimulated to open with chemical (ACh or norepinephrine)
What is initial depolarisation?
This is when local potentials cause local depolarisation from Na+ (sodium) influx through ligand/chemical gated channels
What is rapid depolarisation?
When local depolarisation threshold is reach and voltage-gated Na+ channels open, this causes rapid depolarisation to spread down the axon in a ‘Mexican wave’ like fashion.
What is repolarisation
When Na+ (sodium) channels close at maximum depolarisation (+30mV), and voltage-gated K+ (potassium) channels open which let out K+, repolarising the cell.
What is hyperpolarisation?
This is when K+ (potassium) channels overshoot and the membrane potential becomes more negative than the resting membrane potential (RMP)
How is the resting membrane potential then restored?
The Na+ and K+ ATPase to around -70mV
What is the absolute refectory period?
This is the period where is it IMPOSSIBLE to send another action potential.
- The inactivation gates of the Na+ (sodium) channels lock shut for a time after they have opened so no Na+ (sodium) will pass through.
- NO SODIUM = NO DEPOLARISATION = NO ACTION POTENTIAL
What is the relative refactory period?
This is the period where is it REALLY HARD to send an action potential.
- The period of time after the absolute refactory period, when the inactivation gates are open again.
- However the cell is still hyperpolarised after sending an action potential, so it will take even more positive ions than usual to reach the threshold potential.
- BIG GRADED POTENTIAL NEEDED FOR AP TO BE GENERATED
What are the 3 ways to enhance the speed of an action potential?
- Size - bigger diameter = faster
- Sheath - myelinated = faster (insulation prevents loss of ions)
- Saltatory conduction - Nodes of Ranvier (between myelin) allow the action potential to ‘jump’ from node to node down the nerve = faster.
What is chemical transmission?
Involves neurotransmitters and gated membrane channels.
- ACh is the neurotransmitter involved at the neuromuscular junction (NMJ)
- When ACh binds to the gated channels in post-synpatic membrane this allows the channel to open and for the influx of ions.
What does neuron - neuron transmission involve?
Pre-synaptic and post-synaptic neurons & regulatory neurons.
- This is the transmission of action potentials from neuron to neuron.
- —> Also involved summation.
What does NMJ transmission involve?
Pre-synaptic neuron & post-synaptic muscle fibre.
- The transmission of action potentials in neuron to depolarise (ESPS) or hyperpolarisation (IPSP) of the muscle fibre.
- —-> No summation, no axon hillock!! “absolute” and creates an ESPS always.
Critical components of a chemical synapse:
- Pre-synaptic neuron
- Synaptic cleft
- Post-synaptic neuron or muscle fibre
Grade depolarisations…?
Synaptic transmission doesn’t always create ESPs
- Excitatory (ESPs) or Inhibitory (IPSP) post-synaptic potentials may be made.
- —-> occur within milliseconds
What are ESPs?
When there is an influx of positively charged Na+ (sodium) ions causing depolarisation.
- The membrane potential becomes more positive than the RMP
What are IPSPs?
When there s an efflux (outflow) of positively charged K+ (potassium) ions causing hyperpolarisation
—-> The membrane potential becomes more negative than the RMP
What is the summation of ESPs and IPSPs?
This is when these graded potentials are added together/cancel out.
- If the resting membrane potential is above the threshold and action potential can be generated in neuron - neuron synaptic transmission
What is spatial summation?
About space.
- The closer the graded potential (EPSPs) are on the membrane the more likely it is for a large enough depolarisation to be created to reach threshold and produce an action potential.
What is temporal summation
About time.
- The faster the graded potentials came into the axon hillock the greater the potential created and more likely that it will reach threshold and create nd action potential.
- The time delay between 2 graded depolarisations matters. If the time delay is too long the graded potentials won’t create a large enough depolarisation to give an action potentials.
Where can the spinal cord be found?
Spinal cord lies within a sack made of the meninges, located within the spinal canal of the vertebrae. This meningeal sack is filled with cerebrospinal fluid (CSF)
What is the Conus medullaris?
The tapered cone like end of the spinal cord (this is non-neural tissue)
What is film terminale?
Fibrous, non-neural tissue which extends from the conus medullaris to the end of the spinal cavity - anchors the spinal cord.
- Prevents movement and change.
How many pairs of nerves does the spinal cord have?
31 pairs of spinal nerves. 8 - cervical spinal nerves 12 - thoracic spinal nerves 5 - lumbar spinal nerves 5 - sacral spinal nerves 1 - coccygeal spinal nerves
Spinal cord consists of..?
- Central canal
- Dorsal root (posterior)
- Ventral root (anterior)
- Inner grey matter (butterfly shaped
- Outer white matter
Organisation of informational flow –> Doral (posterior)
Sensory, afferent information comes into the dorsal aspect of the spinal cord from the PNS.
What happens if something in the pathway is damaged (dorsal, sensory afferent info flow)
There will be a loss of sensation to the region’s this pathway supplies (on the same side only)
Informational flow - ventral (anterior)
Motor / efferent information goes out of the ventral aspect of the spinal cord into the PNS.
What happens if damage occurs to the ventral horn.
Produces paralysis of muscles supplied by the somatic motor neurons from the spinal cord segment affected on the same side only
What is the dorsal ramus?
- Efferent (motor) output to the BACK
- Afferent (sensory) input from the BACK
What is the ventral ramus?
- Efferent (motor) output to the ventral body.
- Afferent (sensory) input from the ventral body.
What are rami communicants?
- They connect sympathetic ganglia to the spinal nerves
- Contain nerve fibres of the sympathetic nervous system.
- Only exist T1 - L2
What are the 3 layers of connective tissue in the peripheral nerves?
- Axons - may be myelinated or not. All covered in endoneurium.
- Fasicles - Bundles of axons. Covered in perineurium
- Nerves - Groups of fascicles and blood vessels. Covered in epineurium.
What is the functions of meninges? And the 3 layers of the meninges?
Protective covering for the brain. The three layers are;
1. Dura mater 2. Arachnoid mater 3. Pia mater
What is the Dura mater?
Forms the outer layer of the meninges.
- Is dense fibrous and tough. Composed of an outer periosteal layer and an inner meningeal layer.
- –> Venous sinuses run between these two layers (where 2 layers of dura seperate)
Two layers of the Dura mater?
Periosteal layer & inner (meningeal) layer
What is arachnoid mater?
Spider like, located deep to the dura and superficial to the Pia. It doesn’t extend into the sulk unlike the Pia
—-> Contains sub-arachnoid space.
What is the sub-arachnoid space?
Blood vessels
Found between the Pia mater and the arachnoid space.
Filled with cerebrospinal fluid
What is the Pia mater?
Inner layer of the meninges.
- Transparent and delicate.
- Blood vessels in the sub-arachnoid space sit on top of the Pia
- Pia mater adheres to the brain following the gyro (hills) and dipping down into the sulci (valleys)
Ventricular system features?
A network of interconnected spaces within the brain.
—> Filled with CSF, provides support and cushioning, transports waste
Features of the ventricles…?
- Lateral ventricles
- Third ventricle
- Cerebral aqueduct
- Fourth ventricle
- Central canal
