Overview of PNS Flashcards
define nucleus (plural: nuclei) (in terms of neuronal nomenclature)
nucleus= A group of functionally related nerve cell bodies in the CNS. (NOT the nucleus of a single cell!)
e.g. Inferior olivary nucleus, nucleus ambiguus, caudate nucleus
define column (neuronal nomenclature)
Column= In the spinal cord, a group of functionally related nerve cell bodies that form a longitudinal column extending through part or all of the length of the spinal cord.
e.g Clarke’s column
define Tract or fasciculus (fasciculi)
Tract or fasciculus (fasciculi)= A bundle of parallel axons in the CNS (fasciculus is Latin for “bundle”)
e.g. Optic tract, corticospinal tract, medial longitudinal fasciculus, fasciculus gracilis
=spinal tracts are bundles of axons in CNS, these bundles are organised into specific groups with specific functions forming the tracts
ASCENDING TRACTS= conduct sensory info up to brain
DESCENDING TRACTS= motor instructions down the cord
define nerve, ramus (rami), nerve root
A bundle of axons or nerve fibres. A typical peripheral nerve may have many thousands of individual nerve fibres of many different diameters
what vertebral level does the spinal cord end at
The spinal cord ends around L1/L2, consequently, the caudal nerve roots below the first lumbar root form the cauda equina.
If the sensory loss corresponds to multiple dermatomes the damage is more likely to be the ____________ nerve
If the sensory loss corresponds to multiple dermatomes the damage is more likely to be the peripheral nerve
where is a lumbar puncture performed and why
Lumbar puncture (sampling of cerebrospinal fluid) performed between L3-L4 or L4-L5 to avoid spinal cord
what are the symptoms of cauda equina syndrome
- Cauda equina syndrome
- S = saddle anesthesia (numbness and loss of sensation in the buttocks, perineum, and inner surfaces of the thighs)
- P = pain
- I = incontinence (fecal + urinary)
- N = numbness
E = emergency
_________ MATTER IS WHERE THE NEURONS SYNAPSE + TRANSMIT INFO TO Each other
GREY MATTER IS WHERE THE NEURONS SYNAPSE + TRANSMIT INFO TO Each other
what do the following sensory receptor sense for:
1) root hair plexus
2) free nerve ending
3) meissner corpuscle (encapsulated)
4) pacinian corpuscle (encapsulated)
5) ruffini ending (encapsulated)
6) merkel disc
- Root hair plexus
- Very sensitive mechanoreceptors for touch
- Free nerve ending
- Temperature, mechanical stimuli = pain
- Meissner corpuscle
- Discriminatory touch, sensitive for shape and textural changes
- Pacinian corpuscle
- Vibration and deep pressure
- Ruffini ending (bulbous corpuscle)
- Skin stretch and sustained pressure/movement
- Merkel disc
Pressure, position (deep static touch features)
What kind of neuron detects linear head position
the OTOLITH organs detect linear forces acting on the head, whether by static displacement of hair bundles due to gravity or by transient displacement of hair bundles due to linear accelerations, and this information is preserved in the firing rate of vestibular axons.
Which one of these demonstrate slow adaptation:
* merkel nerve endings
* pacinian corpuscles
- Some neurons the magnitude of the generator potential decays
○ Slow adaptation = Merkel nerve endings □ Good for coding sustained stimulus and its intensity for entire duration ○ Rapid adaptation = Pacinian corpuscles
Good for coding changes in stimulus intensity but not duration
what do golgi tendon organs detect?
muscle tension receptors (proprioceptors)
Aα group Ib
what do muscle spindles detect?
Muscle spindles=
* they’re Proprioceptors
* that are Muscle length receptors
* 5-10% of all neurons in DRG
Aα group Ia
what is the difference between a generator potential vs. an action potential
- Generator (receptor) potential (can potentially become AP if stimulus large enough)
- In the receptor (e.g. sensory dendrites in skin)
- Graded
- Does not obey the all or none rule (it grades how strong stimulus is)
- Can be summated
- Unpropagated
- Action potential
- In the sensory nerve fibre
- Not graded
- Obeys all or none rule
Not summated
what is summation?
Summation is the additive effect of electrical impulses in multiple numbers coming on a neuromuscular junction. A neuromuscular junction is the junction between a nerve cell and a muscle cell. Individually these stimuli can not generate a response, but together they can generate a response.
define propagation
propagation: The movement of signals between neurons.
what are chemoreceptors
Chemoreceptors:
Free nerve endings respond to chemical stimulus
Changes in oxygen, pH, peptides, glucose and salt in extracellular space
Free nerve endings in skin can also respond to mechanical stimuli
Polymodal
which part of the dermis are the cold vs hot receptors found, also explain why when you move your hand from cold to warm water u get a burning sensation?
Thermoreceptors – small knobs on free nerve endings
Varying degrees of heat
Cold receptors 10-40oC (50-104oF) superficial dermis
Hot receptors 32-48oC (90-118oF) deep dermis
Temperatures outside these ranges are detected as nociceptors - pain
When you put your finger into cold water, cold receptors depolarize quickly, then adapt to a steady state level which is still more depolarized than the steady-state. Warm receptors do the opposite: hyperpolarize quickly, then adapt to a slightly hyperpolarized state. When you move your finger from cold to warm water, cold receptors (which are already slightly depolarized), don’t respond very strongly. Warm receptors do, and the response is stronger than normal, because they are slightly hyperpolarized. The brain perceives the warm water as hot because it is receiving more information from hot receptors than from cold.
The opposite response is observed from the thermoreceptors in the finger that is moved from hot to cold (greater response from cold receptors than warm).
The major point is that most receptors (including thermoreceptors) respond most strongly to a CHANGE in stimulus. Therefore a preceding experience that hyperpolarizes the receptor will cause the brain to interpret a new depolarizing stimulus as being stronger than if it “actually” is
how do u work out the conduction velocity for myelinated fibres?
For myelinated fibres velocity = 6 x diameter in µm
what is glabrous skin
Glabrous (nonhairy) skin surfaces (palms of the hands, soles of the feet, face, and ears) constitute a small percentage of total body surface area but contain specialized vascular structures that facilitate heat loss.
- Glabrous skin is used for tactile discrimination
- Smaller size – improves ability to localise stimuli
Receptive fields are larger on skin not used for tactile discrimination
- Smaller size – improves ability to localise stimuli
in glabrous (hairless) skin, free nerve endings are present, as are Merkel’s discs and Meissner’s corpuscles. The latter two receptors have small receptive fields and help to discriminate the spatial relationship of stimuli. This ability to discriminate is well developed on the fingertips.
when a peripheral nerve is damaged, can it regenerate?
- Peripheral nerve axons (fibres) can regenerate
- Approx 1.5-3mm a day from point of injury to peripheral target
- Schwann cells can proliferate and remyelinate axons
- When peripheral nerve is cut:
- Distal part disconnected from cell body degenerates
○ Macrophages remove debris and dead cells - Schwann cells unwrap and go back into cell cycle to proliferate
- New Schwann cells form a line of cells lining endoneurial sheath
Proximal end of nerve fibres form growth cones that grow down the sheath
- Distal part disconnected from cell body degenerates
