Nervous System Flashcards
What are the 2 major components of the nervous system?
central nervous system (CNS)
peripheral nervous system (PNS)
What makes up the CNS?
the brain and spinal cord
What are the 2 types of components of the PNS?
sensory components
motor components
What is included in the sensory components of the PNS?
sensory ganglia and nerves
sensory receptors
What type of stimuli affect the sensory components of the PNS?
internal and external stimuli
What type of neurons are involved in the sensory component of the PNS?
afferent neurons
What are the 2 categories of motor components of the PNS?
somatic
visceral (aka autonomic)
What is involved in the somatic motor components of the PNS?
motor nerves
What do motor nerves of the PNS effect?
skeletal muscle movement
What is involved in the visceral motor components of the PNS?
autonomic ganglia and nerves
What do the visceral motor components of the PNS effect?
effectors:
smooth muscle, cardiac muscle and glands
What type of neurons are involved in the motor component of the PNS?
efferent neurons
What are the 2 major types of neurons in the PNS? what do they do, broadly?
afferent neurons sense changes to internal and external environment
efferent neurons receive signals to cause effects on the motor components
Describe the organization of the nervous system (direction of signaling and components)
in the PNS, afferent neurons sense a change to the internal/external environment and signal to the sensory components (sensory ganglia and nerves, sensory receptors) which send a signal to the CNS (brain and spinal cord)
the brain and spinal cord send signals to the motor components of the PNS (somatic motor nerves and visceral autonomic ganglia and nerves)
the motor components of the PNS send signals to the effectors (skeletal muscles, smooth muscles, cardiac muscles, and glands) via efferent neurons
What is grouped together to make the PNS?
the afferent and efferent divisions
What is grouped together to make the CNS?
the integrating centers (brain and spinal cord)
What is the overall function of the afferent division of the PNS?
to send signals from the PNS to the CNS
What happens when a signal is received from the afferent division of the PNS by the CNS?
the brain and spinal cord integrate the signal and send messages to the efferent division of the PNS which has different effects on the body
What type of movement does the somatic nervous system component of the efferent division of the PNS cause?
voluntary movement of the skeletal muscle
What type of movement does the visceral/autonomic nervous system component of the efferent division of the PNS cause?
involuntary movement of smooth and cardiac muscles, and has effects on glands
What is the enteric nervous system?
it’s associated with the gut and is regulated separately
This basic organization of the nervous system is based on animals with what type of symmetry?
bilateral
Which animals are an exception to this organization of the nervous system into afferent sensory, integrating, and efferent motor divisions?
cnidarians (ex. sea anemones and jellyfish)
Describe the Cnidarian nervous system
it’s one interconnected nerve net
neurons are distributed throughout the body and are not specialized into different divisions like the afferent sensory, integrating, or efferent motor
neurons can have APs in both directions because they’re not specific
complex behaviours are still observed
What, compared to vertebrates, is different about how APs spread in the nervous system of Cnidarians?
Cnidarians can have APs in both directions, whereas in vertebrates APs are unidirectional
What animal group does not have a nervous system at all?
sponges (Porifera)
The organization of the nervous system into afferent, integrating, and efferent divisions is most common in animals with what anatomical features?
cephalization
except for Cnidarians and Echinoderms which do not have cephalization but do have nervous systems
Which animal groups lack cephalization but still have complex nervous systems?
Cnidarians and Echinoderms
T or F: higher complexity of nervous system = more neurons and more synapses
true
more synapses = more integration of info = more complex behaviour
What does a complex nervous system suggest about memory?
memories are stored in synapses, so if there’s more synapses in a more complex system, there’s higher potential for learning
What makes the CNS in vertebrates unique?
highly cephalized
hollow dorsal nerve cord (spinal cord)
CNS is encased in bone or cartilage
What part of the nervous system in vertebrates is encased in cartilage or bone?
the CNS (brain and spinal cord)
What part of the nervous system extends into the periphery of the body?
the PNS which is made up of the nerves external to the CNS
What are the 5 major nerve types that project from the spinal cord in vertebrates?
going from the brainstem down the spinal cord there’s:
cervical nerves
thoracic nerves
lumbar nerves
sacral nerves
coccygeal nerves
What are cranial nerves?
they extend directly from the skull
there’s 13 pairs labelled with roman numerals
some are afferent and some are efferent
What types of functions do the cranial nerves involve?
sensory and motor info
Give some examples of the cranial nerves
olfactory = olfaction
optic = vision
facial = taste, eye muscles, salivary glands
Where do spinal cord nerves enter and extend from?
between adjacent vertebrae
What are spinal cords named for?
the region of the vertebral column that they originate from
cervical
thoracic
lumbar
sacral
coccygeal
What are the broad functions of the nerves that extend from the spinal cord?
they send sensory info to the spinal cord and receive motor info from the spinal cord
Which side of the spinal cord (dorsal or ventral) does the sensory info from the peripheral nerves travel?
dorsally
Which side of the spinal cord (dorsal or ventral) does the motor info from the CNS travel to the peripheral nerves?
ventrally
What two types of tissue do the brain and spinal cord contain?
grey matter
white matter
What makes up grey matter?
neuronal cell bodies
Where is grey matter located in relation to white matter in the brain?
grey matter is the perimeter (surface) of the brain, surrounding the white matter
What makes up white matter?
axons and their myelin sheaths
Where is white matter in relation to grey matter in the brain?
white matter is the internal part of the brain which is surrounded (external surface) by grey matter
Where are grey matter and white matter located in relation to each other in the spinal cord?
the grey matter is internal and the white matter surrounds it
T or F: the CNS is not isolated but it is protected
false
it’s isolated AND protected
What 4 things protect the CNS?
the skull and vertebral columns
meninges
cerebral spinal fluid (CSF)
blood-brain barrier
Why is protection and isolation of the CNS critical for survival?
the CNS does not regenerate if damaged so protecting it from damage is key
What are meninges?
connective tissues (membrane layers) that surround the brain and spinal cord (CNS)
How does the number of meninges vary depending on animal taxa?
the number of layers varies
ex. fish have one layer
amphibians, reptiles and birds have 2 layers
mammals have 3 layers
what is cerebral spinal final (CSF)?
fluid that fills the spaces within the CNS to be a shock absorber
CNS floats in it
What is the blood-brain barrier?
the brain capillary endothelium has tight junctions with glial cells (astrocyte endfeet and pericytes) that prevent free travel of solutes from brainstem into the CSF
What are glial cells?
non-neuronal cells in the CNS
What is the function of the blood-brain barrier?
to protect the brain from harmful substances and immune cells
T or F: the blood brain barrier is completely impermeable and nothing transports through it
false, glucose and amino acids can be transported in
What can be transported into the brain/through the blood brain barrier? and at which parts of the brain?
glucose and amino acids
pineal gland, pituitary gland, and parts of the hypothalamus are semi-permeable
What are the 3 cranial and spinal meninges in mammals?
from top of skull to bottom:
dura mater
arachnoid mater
pia mater
What is an extension of the spinal cord?
the brain
What are ventricles?
cavities in the brain that are filled with cerebral spinal fluid
What are the 4 primary brain vesicles (major brain regions)?
anterior/rostral
forebrain
midbrain
hindbrain
spinal cord
posterior/caudal
what are the 6 secondary brain vesicles found within the primary brain vesicles?
anterior/rostral
telencephalon
diencephalon
mesencephalon
metencephalon
myelencephalon
spinal cord
poster/caudal
What are the 7 major brain components?
anterior/rostral
olfactory bulb
cerebral cortex
thalamus and hypothalamus and pituitary
midbrain
cerebellum and pons
medulla
spinal cord
posterior/caudal
What secondary brain vesicles make up the forebrain?
forebrain is divided into the telencephalon and the diencephalon
What components of the brain make up the forebrain?
olfactory bulb and cerebral cortex in the telencephalon
thalamus (dorsal) hypothalamus (ventral) and pituitary (ventral) in the diencephalon
What components of the brain make up the hindbrain?
the cerebellum which is dorsal to the pons (ventral) in the metencephalon
the medulla in the myelencephalon (rostral to the metencephalon)
What are the 3 regions of the hindbrain (rhombencephalon)?
Pons
cerebellum
medulla oblongata
Describe the pons (location, function)
located in the hindbrain, rostral to the medulla and ventral to the cerebellum
they are the pathway between the medulla, cerebellum and forebrain
function in alertness and initiation of sleep and dreaming, also motor control due to its connection to the cerebellum
Describe the cerebellum (location, function)
located in the 2 hemispheres at the back of the brain, dorsal to the pons, rostral to the medulla
functions in motor coordination
What proportion of brain neurons does the cerebellum contain?
~1/2
What is a pathology related to the cerebellum?
ataxia
related to motor coordination
Describe the medulla oblongata (location and function)
located at the top of the spinal cord, caudal to the cerebellum and pons
functions in breathing, heart rate, diameter of blood vessels and blood pressure regulation
includes the pathways between the spinal cord and the brain
Which neuron pathways does the medulla include?
pathways that run from the spinal cord to the brain
What is the function of the midbrain? Where is it located?
the midbrain is rostral to the pons and cerebellum and caudal to the thalamus and hypothalamus
it’s responsible for coordinating and initiating reflexes in response to auditory and visual signals
T or F: the midbrain is the same size and has the same level of function in all vertebrates
false, it’s size and function are reduced in mammals compared to fish and amphibians
In mammals, how is the midbrain divided? what functions do these divisions play?
inferior colliculi for responses to auditory input
superior colliculi for response to visual inputs
What is the midbrain sometimes grouped in with? what is this unit called?
the pons and medulla to form the brainstem
What is the brainstem?
the midbrain + pons + medulla
What other components are located in the midbrain?
the substantia nigra and VTA
What is the major function of the forebrain?
processing and integrating sensory info and then coordinating behaviour
What are the 5 regions of the forebrain?
cerebrum
hippocampus
thalamus
hypothalamus
limbic system
Where is the hypothalamus located?
at the base of the forebrain, ventral to the thalamus
What is the major function of hypothalamus?
to maintain homeostasis
What are some examples of the physiological variables the hypothalamus is involved in regulating to maintain homeostasis?
body temperature
thirst
hunger
reproduction
renal function
blood pressure
circadian rhythm
How does the hypothalamus help maintain homeostasis?
by interacting with the autonomic NS and regulating pituitary hormones
What is the limbic system?
a group of connected structures that are located between the cortex and the rest of the brain
What are the major functions of the limbic system?
involved in regulating emotions, motivations and memory
What is another term for the limbic system?
the emotional brain
What are components are included in the limbic system?
the hypothalamus
amygdala
hippocampus
olfactory bulbs
nucleus accumbens
cingulate cortex
What is the amygdala responsible for?where is it found?
aggression and fear responses
part of the limbic system
what is the hippocampus responsible for? where is it found?
commits short-term memories into long-term memory
found in the limbic system
What are the olfactory bulbs for? where is it found?
sense smell
limbic system
what is the nucleus accumbens for? where is it found?
related to rewards and addictions
limbic system
what is the cingulate cortex responsible for? where is it found?
executive function, decision making, motivation, planning
limbic system
describe the thalamus (location, function)
large grey matter region above the hypothalamus
functions:
receives info from limbic system and involved in all senses except smell
sends sensory info (somatosensory, visceral, auditory, visual) to cortex
major function: regulating sleep and wakefulness
Describe the cerebrum (function, location)
outer layer is the cerebral cortex
divided into two hemispheres:
- left side to control right side of body
- right side to control left side of body
ie., neurons innervate the opposite side of the body
What side of the body does the right cerebral hemisphere control?
the left side of the body
What side of the body does the left cerebral hemisphere control?
the right side of the body
Where do the cerebral neurons innervate the opposite side of the body?
the corpus callosum
describe the cerebral cortex (location, function)
surrounds the cerebrum
most anterior
processes (integrates and interprets) sensory info and triggers voluntary movement
involved in cognitive functions like planning and decision making
What part of the brain has replaced the midbrain for functions in lower vertebrates?
the cerebral cortex
What is the iso- or neocortex? what is its function?
the outermost layer of the cerebral cortex
required for cognition and higher brain functions
What are gyri (pl.; gyrus s)?
folds in the iso- or neocortex
what are sulci (pl) or sulcus (sin)?
the grooves in the iso- or neocortex
More advanced animals have a higher or lower concentration of gyri and sulci? explain
higher because this increases surface area = more neurons
How many layers are in the cortex? how do they differ?
6 distinct layers that differ in shape, density, and number of connections
What type of neurons have long range projections and which layers of the cerebral cortex do they exist in?
2/3, 5, and 6 layers have pyramidal neurons
What type of neurons have short range projections (local) and which layers of the cerebral cortex do they exist in?
all layers have interneurons
How is the cortex divided?
into cortical lobes
What are the cortical lobes?
frontal
parietal
occipital
temporal
How are the cortical lobes named?
after their function or bones which overlap them
What divides the frontal lobe from the partietal lobe?
the central sulcus (major groove in the cortex)
Who developed the concept of somatotopic organization of the cerebral cortex and what is it?
wilder penfield and herbert jasper
topologically mapped out how each part of the cortex either controls a specific part of the body through motor output or receives sensory info from
On the somatotopic organization of the cerebral cortex map, what does it mean if a body part is drawn larger?
the part of the cerebral cortex which controls this part of the body occupies a larger space and has more neurons
What is the somatosensory system?
the pathway for sensory information received in the body is transmitted to the brain
made up of 3 subsystems to regulate sensations such as touch, pressure, limb position, temperature, pain
What are the 3 subsystems of the somatosensory system?
cutaneous mechanoreceptors
proprioception
pain and temperature
What detects the sensations sensed by the somatosensory system? where do they transmit this info?
receptors in the skin, muscles, and tendons
the sensory signals are transmitted to the CNS
What type of sensations does the cutaneous mechanoreceptor subsystem of the somatosensory system receive?
touch
vibration
pressure
from receptors on the skin
What type of sensations does the proprioception subsystem of the somatosensory system receive?
limb position
load (weight) on joints
from receptors in muscles, tendons and joints
What are dorsal root ganglia?
the sensory receptors (where cell bodies of afferent fibers are) for the body
What are cranial nerve ganglia?
sensory receptors of the head
where the cell bodies of afferent neurons are
what is a dermatome?
the region a single dorsal root ganglion innervates and its associated spinal nerve
ex. cervical, thoracic, lumbar, sacral
How are mechanosensory afferents transduced?
a stimulus changes the permeability of cation (mechanosensitive) channels on the membrane of afferent nerve endings
mechanoreceptors on afferent neurons sense pressure and the membrane stretches to open cation (Na+) PIEZO channels
influx of Na+ depolarizes membrane potential and triggers action potential if strong enough
What is the name of the channels involved in mechanosensory afferent neuron transduction?
PIEZO channels for Na+ or other cations
What are some types of mechanoreceptors?
Merkel, Meissner, Pacinian, Ruffini cells
How do somatosensory afferents differ?
axonal diameter, conduction velocity, size of receptive field
what is used to determine the size of a somatosensory afferent neuron’s receptive field?
the 2 point discrimination
the smallest distance between 2 points before they become 1
What body parts would have somatosensory afferent neurons with the smallest receptive fields? the largest? why?
smallest: fingers
largest: shoulders, back, arms
it’s more important to have neurons in parts of the body that are critical to function like grabbing and holding objects
Which somatosensory afferent neurons have the largest axon diameter and conduction velocity? smallest?
largest
proprioception (muscle spindle and golgi tendon organ)
cutaneous (Merkel, etc.)
pain, temperature, itch (free nerve endings)
smallest
What are the 2 types of temporal dynamics that influence somatosensory afferents?
rapidly adapting
slowly adapting
Describe rapidly adapting somatosensory afferent neurons
trigger action potentials only when the stimulus is changed (ex. at the application of a stimulus and at the removal of a stimulus, but not during the stimulus)
Describe slowly adapting somatosensory afferent neurons
trigger action potentials for the duration of the stimulus
What type of info (static vs. dynamic) do slowly adapting mechanoreceptors provide?
static
What type of info (static vs. dynamic) do rapidly adapting mechanoreceptors provide?
dynamic
Where in the layers of the skin (epidermis, dermis, subcutaneous), do each of the mechanoreceptors reside (free nerve endings, Meissner, Merkel, Ruffini, Pacinian)?
free nerve endings are closest to the surface in the epidermis
Meissner corpuscle are in epidermis, below free nerve endings
Merkel cells are in epidermis/dermis below Meissner
Ruffini are in dermis
Pacinian corpuscle are in subcutaneous layer
Are most afferent fibers coated in specialized receptor cells or are they mostly free nerve endings?
most of them are covered in mechanoreceptors (specialized receptor cells)
What is the purpose of afferent fibers being covered in mechanoreceptors?
they lower the threshold for detecting somatic stimulation like pressure
Are afferents with mechanoreceptors more or less sensitive to sensory stimulation than free nerve endings?
more sensitive than free nerve endings
what types of mechanoreceptors are slowly adapting?
merkel cell afferent
ruffini afferent
What types of mechanoreceptors are rapidly adapting?
meissner and pacinian afferent
Which mechanoreceptor is the most sensitive?
Pacinian afferents
Where are merkel afferents most concentrated? what are they most sensitive to?
fingertips
sensitive to points, edges, curves
function in processing info about form and texture
Which afferent mechanoreceptors are for processing form and texture information? why?
merkel cell afferents because they’re concentrated in the fingertips
Where are Meissner afferents located? what are they sensitive to?
the hand, closest to skin surface
super sensitive
sensitive to textured objects moving across the skin and grip of the hand
WHere are the Pacinian afferents? what are the sensitive to?
they’re located deep in the dermis
sensitive to vibrations through an object when you’re using it
ex. using a knife to cut, using a pen to write, using a tool
Where are the ruffini afferents? what are they sensitive to?
deep in the dermis
sensitive to internal stimuli such as movement of fingers and provide accurate info for finger and hand positioning without having to look
ex. playing a piano, typing
Rate the mechanoreceptors in order of spatial resolution (high to low)
highest:
merkel cell (0.5mm)
Meissner (3mm)
ruffini (>7mm)
pacinian (>10mm)
Describe the cutaneous mechanosensory pathway
sensory information received in body on dorsal side
info from dorsal lower body received in lumbar spinal cord sent ipsilaterally through spinal cord until caudal medulla
at caudal medulla, the info crosses the spinal cord and travels up contralaterally
enters brain ventral posterior
reaches primary somatosensory cortex of cerebrum
What are proprioceptors?
mechanoreceptors that detect body positioning and provide continuous info about limb positions
What are the 2 major groups of vertebrate proprioceptors?
muscle spindles
Golgi tendon organs
What are muscle spindles (location, function)?
a group of proprioceptors in vertebrates located on the surface of skeletal muscles
they monitor the length of muscles and receive information about limb movement and limb positions
muscle spindles are composed of muscle fibers (intrafusal fibers)
Describe the structure of muscle spindles
composed of intrafusal muscle fibres surrounded by sensory afferent groups Ia and II
What function do sensory afferents I and II have regarding muscle spindles?
they coil around the intrafusal muscle fibers that make up muscle spindles
Ia = movement of limbs (rapidly adapting)
II = static limb positions (slowly adapting)
What are golgi tendon organs (location, function)?
a group of vertebrate proprioceptors located at the junction of skeletal muscles and tendons
composed of Ib afferents that are in the collagen fibers of tendons
changes in the tension in the tendon cause stimulation of these receptors
What’s an example of how the golgi tendon organs function?
they cause reflex protective actions for the muscles by causing the arm to let go of a load when the tension is too high on the tendon
protect the tendons and muscles
Describe the proprioceptive pathway
muscle spindles or golgi tendon organs afferents send signal from the lower body into the dorsal spinal cord
signal sent ipsilaterally up spinal cord to synapse in the thoracic spinal cord and travel to the cerebellum
from caudal medulla > medial lemiscus > VPL > primary somatosensory
What is the primary somatosensory cortex?
What layer of the primary somatosensory cortex do mechanosensitive and proprioceptive information project to?
layer 4
What does the primary somatosensory cortex comprise of?
Brodmann’s areas 3a, 3b, 1 and 2
What sends mechanosensitive and proprioceptive info to the 4th layer of the primary somatosensory cortex?
the ventral posterior complex of the thalamus
How is the cerebral cortex organized?
somatotopically
every region of the cortex is associated with a specific body part and controls it by motor output or receives sensory input from it
Which mechanoreceptors in the skin detect pain and temperature?
free nerve endings in the epidermis
T or F: all free nerve endings are unmyelinated
false, some are but some are also myelinated
How is pain transmitted?
at 2 different velocities
first pain
second pain
What is first pain? What type of fibers mediate it?
the sharp, rapidly transmitted pain mediated by myelinated A(delta) fibers
What is second pain? what type of fibers mediate it?
the more delayed, slower transmitted and longer lasting pain
mediated by unmyelinated C fibers
what are nociceptors?
free nerve endings that trigger pain sensation
Do the axons in nociceptors have faster or slower conduction velocities?
slower
Adelta fibers 5-30 m/s
C fibers <2 m/s
What kind of sensations do Adelta fiber nociceptor axons detect?
intense mechanical (pain) or heat stimuli
What kind of sensations do C fiber nociceptor axons detect?
intense mechanical (pain)
warm/cool temperature
chemical stimuli
T or F: nociceptor axons are polymodal - what does this mean?
true, it means they can detect a variety of sensations
What are the channels for pain, heat, and chemical stimuli?
TRPs: Transient Receptor Potential channels - non-selective cation channels
What is the pain pathway?
the anterolateral system
Describe the anterolateral pathway
pain or temperature sensations are received by nociceptors in the lower or upper body and info is passed into the dorsal spinal cord
signal crosses the spinal cord to ventral side and travels contralaterally up the spinal cord
through caudal medulla, rostral medulla, pons, midbrain and reaches the ventral posterior lateral thalamus and the primary somatosensory cortex
Where does the signal detected by nociceptors cross the body? How does this differ from other afferent neurons?
it crosses at the cervical and lumbar spinal cord (almost immediately upon entrance)
whereas other pathways travel ipsilaterally until the caudal medulla where the cross occurs
What branch of the peripheral nervous system is the autonomic nervous system part of?
the efferent branch
What are the 3 types of nervous systems in the autonomic nervous system?
sympathetic
parasympathetic
enteric
Describe the autonomic nervous system
the involuntary response system
involved in homeostasis
composed of the sympathetic, parasympathetic, and enteric systems
Describe the sympathetic nervous system
part of the autonomic nervous system
activated during stress or physical activity
the ‘fight or flight’ response system
Describe the parasympathetic nervous system
part of the autonomic nervous system
activated during periods of rest
the ‘resting and digesting’ system
describe the enteric nervous system
part of the autonomic nervous system
functions independently of the sympathetic and parasympathetic systems
involved in digestion
How does the autonomic nervous system help in maintaining homeostasis?
by balancing the activity of the sympathetic and parasympathetic nervous systems
What are the 3 mechanisms for regulating involuntary functions?
dual innervation
antagonistic action
basal tone
Describe how the autonomic nervous system uses dual innervation to maintain homeostasis
nerves from both the sympathetic and parasympathetic systems are innervating the organs of the body (sending info)
Describe how the autonomic nervous system uses antagonistic action to maintain homeostasis
one of the 2 systems (symp. or para) will be stimulating while the other is inhibiting at any given time
Describe how the autonomic nervous system uses basal tone to maintain homeostasis
there is a constant flow of action potentials carried by autonomic neurons, even during resting periods
Where do the sympathetic neurons originate from along the spinal cord?
the thoracic and lumbar nerves
Where do the parasympathetic neurons originate from along the spinal cord?
the cranial nerves and sacral nerves
Give some examples of antagonistic action by the autonomic nervous system
eye pupils: the parasympathetic system constricts; the sympathetic system dilates
heart: PS slows heart rate; SS increases heart rate and force of contractions
digestive tract: PS increases digestion; SS decreases digestion
Describe the anatomy of autonomic pathways
they have 2 neurons in series
cell body of the first neuron (preganglionic neuron) is in the CNS
preganglionic neuron synapses with postganglionic efferent neuron in the PNS
What are the 3 major anatomical differences between the sympathetic and parasympathetic branches?
- origin of preganglionic neurons:
sympathetic: cell bodies in thoracic and lumbar spinal cord regions
para: cell bodies in cranial and sacral spinal cord regions
- location of ganglia
sympathetic: run close to spinal cord = preganglionic neurons are shorter, postganglionic neurons are longer
para: run close to effector/target organ = preganglionic neurons are longer, postganglionic neurons are shorter
- distribution of effects
sympathetic: preganglionic neurons form synapses with 10+ postganglionic neurons = widerspread effects
para: preganglionic neurons form synapses with < 3 postganglionic neurons = more localized effects
Which branch of the autonomic nervous system has neurons that run closer to the spinal cord? how does this effect the length of preganglionic and postganglionic neurons?
sympathetic
preganglionic neurons are shorter
postganglionic neurons are longer to reach the target organ
Which branch of the autonomic nervous system has neurons that run closer to the target organs? how does this effect the length of preganglionic and postganglionic neurons?
parasympathetic
preganglionic neurons are longer
postganglionic neurons are shorter
Which neurotransmitter do the preganglionic neuron in both the sympathetic and parasympathetic systems release? what receptor does the postganglionic neuron have?
the preganglionic neuron releases acetylcholine (ACh) and the postganglionic neuron has nicotinic receptors for binding ACh
What does the release of ACh by the preganglionic neuron and binding of ACh by the postganglionic neuron cause in the postganglionic cell? in both sympathetic and parasympathetic systems
nicotinic ACh receptors are ligand-gated ion channels
binding of ACh opens Na+ ion channel and rapidly depolarizes the postganglionic cell
always excitatory
How do the neurotransmitters differ between the sympathetic and parasympathetic systems?
parasympathetic:
postganglionic neurons release ACh but target organ has muscarinic ACh G-coupled receptors (not nicotinic receptors) = response is slower and can be excitatory or inhibitory
sympathetic:
postganglionic neurons release norepinephrine that bind to the adrenergic receptors on target organ which triggers a signal transduction pathway
What type of effector organ do efferent motor neurons control?
only skeletal muscles
Where are the cell bodies of motor neurons located (where do they originate)?
only ever within the CNS
How many synapses do efferent motor pathways have between the CNS ganglia and the effector organ? how does this compare to the autonomic nervous system?
only one neuron and one synapse
the sympathetic and parasympathetic nervous system have 2 synapses (one between the preganglionic and postganglionic neurons and one between the postganglionic and effector organ)
What is a result of there only being one synapse between the CNS and the effector organ in efferent motor pathways?
efferent motor neurons can be super long
some axons are multiple meters long
What neurotransmitter do efferent motor neurons release?
only acetylcholine
What is the effect of acetylcholine released by efferent motor neurons on skeletal muscles?
always excitatory - contraction
describe the pathway of efferent motor neurons (corticospinal tract)
motor neurons originate in the CNS and information travels from the primary motor cortext down the ventral side of the spinal cord through the midbrain, pons, middle medulla
90% of signal crosses the spinal cord at the caudal medulla to dorsal side, other 10% remain on ventral
What type of skeletal muscles would efferent motor neurons that track down the ventral corticospinal tract innervate?
muscles related to posture such as abdominal and back muscles
What type of skeletal muscles would efferent motor neurons that track down the lateral corticospinal tract innervate?
muscles in extremities like hands, fingers, legs, etc
T or F: one alpha motor neuron will innervate all the muscle fibers in the target organ
false, one neuron will only innervate a few fibers so many neurons need to be recruited for increased strength of contraction
in what ways can the strength of contraction in skeletal muscles be increased?
by recruiting more alpha efferent motor neurons = increasing stimulation of more muscle fibers
increasing frequency and intensity of stimulation
describe temporal summation
stimuli frequency is increased and the muscle fiber doesn’t have time to relax before next signal causing an increased response
Describe unfused tetanus
stimulation intensity and frequency is increased
response is higher, fluctuates but does not have time to properly relax between contractions
Describe fused tetanus
very high intensity and frequency of stimuli causes no relaxation between contractions
In what context would temporal summation be most likely?
running
In what context would fused tetanus be most likely?
weight lifting
