neurophysiology (nervous system) Flashcards
peripheral nervous system VS central nervous system:
The CNS includes the brain and spinal cord (= brain + spinal cord), while the peripheral nervous system consists of everything else. (cranial nerves, spinal nerves and their roots and branches, peripheral nerves, and neuromuscular junctions = nerves and sensory organs)
somatic VS autonomic nervous system:
he somatic nervous system is responsible for voluntary actions such as scratching an itch. The autonomic nervous system is responsible for most involuntary movements in the body such as digestion
PNS = divided into 3 parts:
SNS : voluntary (skeletal muscles)
ANS: involuntary (smooth muscles)
ENS: “brain” of the gut = GI tract NS
all communicate with CNS
rubrospinal tract:
riginates in the red nucleus and
projects to motoneurons in the lateral spinal cord.
Stimulation of the red nucleus produces activation of flexor
muscles and inhibition of extensor muscles
pontine reticulospinal tract:
originates in nuclei of the
pons and projects to the ventromedial spinal cord.
Stimulation has a generalized activating effect on both flexor
and extensor muscles.
medullary reticulospinal tract:
originates in the medullary
reticular formation and projects to motoneurons in the spinal
cord. Stimulation has a generalized inhibitory effect on both
flexor and extensor muscles.
lateral vestibulospinal tract
riginates in the lateral
vestibular nucleus (Deiters’ nucleus) and projects to
ipsilateral motoneurons in the spinal cord. Stimulation
produces activation of extensors and inhibition of flexors.
tectospinal tract
originates in the superior colliculus and
projects to the cervical spinal cord. It is involved in control of
neck muscles.
pyramidal tracts:
are corticospinal and
corticobulbar tracts
that pass through
the medullary
pyramids and
descend directly
onto lower
motoneurons in the
spinal cord
The ventricular system of the human brain:
- The cerebral ventricles are a series
of interconnected, fluid (CSF) filled
spaces that lie in the core of the
forebrain and brainstem - produced by a modified vascular
structure called the choroid plexus
functions of the CSF:
Protection: the CSF protects the brain from damage by “buffering” the brain. In other words, the CSF acts to cushion a blow to the head and lessen the impact.
Buoyancy: because the brain is immersed in fluid, the net weight of the brain is reduced from about 1,400 g to about 50 g. Therefore, pressure at the base of the brain is reduced.
Excretion of waste products: the one-way flow from the CSF to the blood takes potentially harmful metabolites, drugs and other substances away from the brain.
Endocrine medium for the brain: the CSF serves to transport hormones to other areas of the brain. Hormones released into the CSF can be carried to remote sites of the brain where they may act.
circulation of the CSF (AV drainage)
slide 28
preganglionic VS postganglionic functions:
These neurons are known as preganglionic neurons and travel to ganglia, where they synapse and activate nicotinic receptors on postganglionic neurons using acetylcholine. The postganglionic neurons then travel to the target site and release norepinephrine to activate adrenergic receptors.
neurotransmitters in the autonomic nervous system:
Acetylcholine (ACh)
– used in both the parasympathetic and sympathetic
nervous system (cholinergic nerves)
Norepinephrine (NE) (also referred to as noradrenaline)
– in the periphery used only in the sympathetic nervous
system (adrenergic nerves)
Epinephrine (EPI) (also referred to as adrenaline)
– a hormone released from the adrenal medulla
Acetylcholine is the neurotransmitter at all autonomic ganglia
sympathetic VS para pre + postganglionic neurons:
- Most sympathetic post-ganglionic neurons release norepinephrine to act on adrenergic receptors of target organs. However, there are some exceptions, such as the sweat glands, where acetylcholine is released by post-ganglionic neurons and binds to muscarinic receptors.
(Acetylcholine is released from pre-ganglionic neurons and binds to nicotinic receptors on post-ganglionic neurons.) - the parasympathetic: Pre-ganglionic neurons: Acetylcholine is released from pre-ganglionic neurons and binds to nicotinic receptors on post-ganglionic neurons (similar to the sympathetic system).
Post-ganglionic neurons: Acetylcholine is also released by parasympathetic post-ganglionic neurons, but it acts on muscarinic receptors located on the target organs.
tissue responses define receptors:
Smooth Muscle Responds to ACh and Muscarine
(Muscarinic Cholinergic Receptor)
Skeletal Muscle Responds to ACh and Nicotine
(Nicotinic Cholinergic Receptor)
!! Acetylcholine is the neurotransmitter at all autonomic ganglia !!
muscarinic vs nicotinic receptors (both for AcH)
- Nicotinic receptors function within the central nervous system and at the neuromuscular junction. While muscarinic receptors function in both the peripheral and central nervous systems, mediating innervation to visceral organs
- Nicotinic cholinergic receptors stimulate sympathetic postganglionic neurons, adrenal chromaffin cells, and parasympathetic postganglionic neurons to release their chemicals. Muscarinic receptors are associated mainly with parasympathetic functions and are located in peripheral tissues (e.g., glands and smooth muscle).
you also find adrenergic in (only) sympathetic
Norepinephrine is the neurotransmitter:
at most sympathetic nerve terminals
There are three exceptions
Exceptions in the sympathetic nervous system:
- Sweat glands: Postganglionic sympathetic neurons involved with sweating release acetylcholine. They are called sympathetic cholinergic
neurons - Kidneys: Postganglionic neurons to the smooth muscle of the renal
vascular bed release dopamine
Exceptions in the Sympathetic Nervous system II and III - Adrenal gland: Preganglionic neurons do not synapse in the paravertebral
sympathetic ganglion
» Preganglionic neurons
synapse directly on the
adrenal gland, release
acetylcholine, and activate
nicotinic receptors on the
adrenal gland
» Adrenal glands release
epinephrine and
norepinephrine (4:1) into the
systemic circulation
Ascending VS descending tracts (neurons of spinal cord from neural tracts)
- Ascending: carry sensory input to the brain
- Descending: send motor commands downwards to the body
Local circuit neurons in the
spinal cord gray matte
- Pathways that contact the medial parts of the spinal cord gray matter are Involved (terminate bilaterally)
primarily In the control of posture - Those that contact the lateral parts are involved in the fine control of the distal extremities. (always terminating on the same side of the cord as the cell body)
Reflex arc:
spinal reflexes involve circuits of sensory nerve fibers that feed information to the spinal cord and then connect directly, or via an intermediate neuron, to motor nerve fibers, so that the resulting instructions for movements go directly out from the cord to the relevant muscles and not to the brain, to be activated
what is a dermatome ?
dermatome is an area of the skin in which all
cutaneous fibers track back to the same spinal level
(i.e., they all go into the spinal cord at, say, at C8, which
would define C8 dermatome)
- Cutaneous fibers that all map to the same spinal level =
dermatome but the fibers of the same dermatome may
reach the spinal cord via different cutaneous nerves
skin mechanoreceptors:
- Merkel cell afferents are slowly adapting fibers that account for about 25% of the mechanosensory afferents in the hand. They are especially eriched in the fingertips, and are the only afferents to sample information
from receptor cells located in the epidermis. - Meissner afferents are rapidly adapting fibers that innervate the skin even more densely than Merkel afferents, accounting for about 40% of the mechanosensory innervation of the human hand.
- Pacinian afferents are rapidly adapting fibers that make up 10-15% of the mechanosensory innervation in the hand. Pacinian corpuscles
are located deep in the dermis or in the
subcutaneous tissue; - Ruffini afferents are slowly adapting fibers and are the least understood of the cutaneous mechanoreceptors.
- Ruffini endings are elongated, spindle-shaped, capsular specializations located deep in the skin.
posterior column
consists of two tracts: the
gracile fasciculus and the cuneate fasciculus.
The posterior column tracts convey nerve
impulses for discriminative touch, light pressure,
vibration, and conscious proprioception (the
awareness of the positions and movements of
muscles, tendons, and joints).
myotome:
Each set of spinal nerves
also innervate a certain
set of muscles
spinothalamic tract
onveys nerve impulses
for sensing pain, warmth, coolness, itching,
tickling, deep pressure, and crude touch.
motor direct pathways VS indirect pathways:
Motor direct pathways include the
* lateral corticospinal,
* anterior corticospinal,
* corticobulbar tracts.
They convey nerve impulses that originate in the cerebral cortex and
are destined to cause voluntary movements of skeletal muscles.
Motor indirect pathways include:
* rubrospinal,
* tectospinal,
* vestibulospinal,
* lateral reticulospinal,
* medial reticulospinal tracts.
These tracts convey nerve impulses from the brain stem to cause
automatic movements and help coordinate body movements with
visual stimuli. Indirect pathways also maintain skeletal muscle tone,
Conduction function of the spinal cord
causes of spinal nerve pain:
(when people age), the jelly like material between the discs can dry out, making them thinner, letting the vertebrae move closer to eachother. This is how they can start to pinch a nerve and cause pain where the nerve goes.
- this can also happen with extra lifting
fiber types
Pain can be separated into an early perception of sharp pain and a later sensation that is described as
having a duller, burning quality.
(A) First and second pain, as these sensations are called, are carried by different axons
(B) the selective blockade of the more rapidly conducting myelinated axons that carry the sensation of
first pain
(C) blockade of the more slowly conducting C fibers that carry the sensation of second pain.
anterolateral system functions:
The anterolateral system supplies
information to different parts of the
brainstem and forebrain that
contribute to different aspects of the
experience of pain:
- Sensory discriminative
aspects of pain:
the location, intensity, and
quality of the noxious
stimulation.
- Affective-motivational aspects of pain:
the unpleasant feeling, the fear and anxiety,
and the autonomic activation that accompany
exposure to a noxious stimulus (the
classic “fight-or-flight” reaction
the anterolateral system:
(A) Primary afferents in the dorsal root ganglia send their axons via the dorsal roots to terminate in the dorsal horn of the spinal cord. Afferents branch and course for several segments up and down the spinal cord in Lissauer’s tract, giving rise to collateral branches that terminate in the dorsal horn. Second-order neurons in the dorsal horn send their axons (black) across the midline to ascend to higher centers in the anterolateral column of the spinal
cord.
(B) C-fiber afferents terminate in Rexed’s laminae 1 and 2 of the dorsal horn, while Aδ fibers terminate in layers 1 and 5. The axons of second-order neurons in laminae 1 and 5 cross the midline and ascend to
higher centers.
slide 60
!!!!
sensitisation:
Substances released by damaged tissues augment the response of nociceptive fibers. In addition,
electrical activation of nociceptors causes the release of peptides and neurotransmitters that further contribute to the inflammatory response
peripheral VS central sensitisation:
- Peripheral sensitization results from the interaction of nociceptors with the “inflammatory soup” of substances released when tissue is
damaged. - Central sensitization refers to an immediate onset, activity-dependent increase in the excitability of neurons in the dorsal horn of the spinal cord following high levels of activity in the
nociceptive afferents
slide 62 !!
!! + 63 !!! + 66
Where does the information come from?
RECEPTORS:
- ancient - free nerve endings
* invade the epithelium of the skin and mucosa, occur in the walls of
viscera
* no highly specialized structures around the peripheral processes of
sensory neurons
* pain and temperature, with relatively high threshold
- relatively new - specialized structures
* rather in the dermis and subcutis, in joints, muscles and tendons
* complex structures around the peripheral nerve endings
composed of different cell types including modified Schwann-cells
* low threshold for touch, pressure, vibration, stretch
information exchange in spinal cord:
slide 68 !!!
effectors (muscles and glands)
CNS directly controls skeletal
and visceral striated muscles
through the neuromuscular
junctions: there is no need for
synapses on the periphery.
- Direct Control via Neuromuscular Junction: The neuromuscular junction is the point where the motor neuron communicates directly with the muscle fiber by releasing the neurotransmitter acetylcholine (ACh), triggering muscle contraction.
CNS on smooth muscles and glands:
Axons of autonomic neurons of the CNS terminate in autonomic
ganglia and only the axons of those neurons resting in them will
reach the target organs. Without at least one synapse on the periphery
CNS has no direct influence on smooth muscles and glands.
Nervous system cells: (action)
slide 7
what are neurones ?
cells in nervous tissue
neurones = charged cells, conduct electrical signals to pass information through the body
neurons composition functions:
- neurons communicate with other neurons and tissues by action potential.
- neurones have special processes: dendrites receive input and axons transmit action potential
- some axons = coated with myelin (white sheath)
- gaps in myelin = nodes of Ranvier
- Similar to other cell in body having
nucleus and most organelles in
cytoplasm - different because: Neurons has branches or processes-
dendrites and axon - Have nissl granules and neurofibrillae
- No centrosome- loss power of division
- Contain and secrete neurotransmitters
efferent VS afferent neurones:
- efferent:
- Carry impulses from CNS to
peripheral effector organs e.g.,
muscles/glands/blood vessels - Generally each motor neurons
has long axon and short
dendrites - afferent:
- Carry impulses from periphery to
CNS - Generally each neuron has short
axon and long dendrites
