nervous system pt 2 (sensation, perception, nerves, etc.) Flashcards
sensation
the awareness of a stimulus through sensors; information from the environment will be translated into electrical messages called action potentials
perception
the conscious interpretation, organization, and meaning of the stimulus and this occurs within the cerebrum
what are sensory receptors based on?
the type of stimulus they detect, the location in the body, and the structural complexity
two types of general senses
somatic and visceral senses
difference between general senses and special senses
general senses are those that are distributed throughout the body and have receptor cells within the structure of other organs (somatic or visceral), while special senses are those that have a specific organ devoted to them (ex. ear, nose, etc.)
somatic senses
all tactile senses (touch), pain, and proprioception that detect mechanical stimuli
what are somatic senses associated with?
mechanial stimuli
visceral senses
conscious/subconscious sensation of internal organs that is associated with autonomic function
special senses
olfaction, taste, vision, hearing, equilibrium, and balance
first-order neurons
initial sensory receptors that receive impulses from the skin and preceptors (sensory receptors) and branch diffusely as they enter the spinal cord or medulla oblongata; here they will synapse with second-order neurons
how do first-order neurons synapse with second-order neurons?
first-order neurons will synapse with second-order neurons in the cuneate or gracile nuclei of the medulla oblangata; second-order neurons will then travel to the thalamus
how do second order neurons synapse with third order neurons?
second order neurons will synapse with third in the thalamus and extend to the the somatosensory cortex
3 types of interactions with first-order neurons
free nerve endings, encapsulated nerve endings, and specialized receptor cells
free nerve endings
the dendrites of first-order neurons are exposed directly to the surrounding tissue of the environment without any specialised receptor structure; the bare endings will detect the stimulus directly
what are free nerve endings typically associated with?
detecting pain, temperature, and some light touch
encapsulated endings of first-order neurons
these types are wrapped in a specialised CT and this modifies the sensitivity of the neuron, allowing it to detect specific types of mechanical stimulus more effectively
examples of encapsulated endings
pacinian corpuscles and meissner’s corpuscles
specialised receptor cells
here, the neurons do not directly interact with the external environment, instead they form synapses with specialised receptor cells which will first detect the stimulus and then release neurotransmitters that will activate the first-order neurons; associated with all special senses
example of specialised receptor cells
all special senses; ex. receptor cells such as gustatory (taste) receptors that will release acetylcholine, serotonin and norepinephrine
interceptor
a type of sensory receptor that detects and responds to stimuli from within the body (internal viscera, tissues, and blood vessels) rather than the external environment
function of interceptors
to maintain homeostasis and visceral sensation through responding to internal conditions such as blood pressure, temperature changes, chemical compositions, and stretching of internal organs
examples of interoceptors
baroreceptors, chemoreceptors, and stretch receptors
exteroreceptor
sensory receptors that respond to stimuli arising outside of the body and are located on or near the body’s surface; associated with all special senses and all skin senses
functions of exteroceptors
to detect external stimuli and sensory perception to process sensory information such as touch, temperature, pain, and pressure
examples of exteroceptors
mechanoreceptors, thermoreceptors, photoreceptors, nociceptors, and olfactory receptors
proprioceptors
sensory receptors that respond to stretch in skeletal muscle, tendons, joints, ligaments, and CT surrounding bone and muscle, while also allowing one to be aware of their body position and movement
functions of proprioceptors
body awareness, coordination of movement, and balance and posture
examples of proprioceptors
muscle spindles, golgi tendon organs, and joint receptors
mechanoreceptors
respond to touch, pressure, vibration, and stretch
thermoreceptors
sensitive to changes in temperature
nociceptors
sensitive to pain causing stimuli, ex. extreme hot or cold, excessive pressure, and inflammatory chemicals
chemoreceptors
respond to chemicals, ex. smell, taste, and changes in blood chemistry
photoreceptors
respond to light energy, ex. retina
osmoreceptors
respond to the osmolarity of the ECF
adaptation
how quickly you become acclimated to a sensation when the stimulus is sustained; 2 types
2 types of adaptation
rapidly adapting receptors and slowly adapting receptors
rapidly adapting receptors
respond quickly to a change in stimulus but stop firing or reduce their firing rate if the stimulus is sustained; specialised in detecting changes in the environment such as the start or end of a stimulus
types of stimulus associated with rapidly adapting receptors
stimulus like temperature or smell; non-life threatening stimuli
examples of rapidly adapting receptors
Pacinian and meissner’s corpuscles
slowly adapting receptors
continue to fire at a relatively constant rate as long as the stimulus is present; they provide continuous information about a sustained stimulus and do not adapt quickly to constant input
types of stimulus associated with slowly adapting receptors
life threatening stimuli like pain or extreme temperatures
three steps in a typical somatic sensory pathway
first-order neuron, second-order neuron, and third-order neuron
what are interneurons in the ascending pathway
second and third-order neurons
lower motor neurons
the only neurons that directly control skeletal muscle; function as the final common pathway for transmitting motor commands to muscle, resulting in movement
where do lower motor neurons receive their input from?
upper motor neurons (rarely) or local circuit neurons
where are lower motor neurons found?
the anterior horn of the spinal cord and the motor nuclei of cranial nerves in the brainstem
upper motor neurons
synapse with local circuit neurons and rarely with LMNs; these initiate and plan voluntary movements through sending signals from the brain to LMNs
2 pathways to know for motor output
corticospinal tract and corticobulbar tract
where are upper motor neurons located?
the primary motor cortex; precentral gyrus and premotor cortex
basal nuceli
large group of CNS neurons that are implicated in emotion and habitual behaviour; responsible for the initiation and regulation of voluntary movements by modulating UMN activity
where are basal nuclei located?
deep in the brain such as the caudate nucleus and putamen
similarities between the direct and indirect motor pathway
both are pathways in which the brain controls voluntary and involuntary movement, and both involves UMNs
direct motor pathway
involves the direct linkage of axons from the cerebral cortex to the end of a tract in the spinal cord without any intermediary relays; ex. corticospinal (lateral and anterior) and corticobulbar
where will the synapse occur in a direct pathway?
anterior horn of the spinal cord with a LMN
another name for direct motor pathway
pyramidal system
tracts involved in the direct motor pathway
corticospinal and corticobulbar tracts
what type of movement does the direct motor pathway result in?
fast and fine (skilled) movements
indirect motor pathway
complex and multisynaptic pathway that involves input from basal nuclei, cerebellum, and cerebral cortex, which indirectly influences LMNs through these relays (includes all motor pathways except from pyramidal pathways)
what do indirect motor pathways regulate
axial muscles, muscles controlling coarse limb movements, and head, neck, and eye movements
tracts involved in the indirect motor pathway
rubrospinal, reticulospinal, vestibulospinal, and tectospinal tracts
corticospinal tract
a major motor pathway that controls voluntary movements of skeletal muscle; it originates in the primary motor cortex and descends through the brain and the spinal cord where it synapses with LMNs
lateral corticospinal tract
located in the lateral white matter of the spinal cord and controls fine, precise and voluntary movements, most often in the hands and fingers; majority of these tracts decussate at the medullary pyramid
anterior corticospinal tract
located within the anterior white matter of the spinal cord; it primarily controls the axial muscles of the shoulders, trunk, and neck that are involved in posture in balance; these rarely decussate at the medullary pyramids
PNS
provides link from and to the outside body from the world; includes all neural structures outside of CNS such as sensory receptors, peripheral nerves, associated ganglia, and efferent motor endings; further branches into sensory division and motor division, then to ANS
ANS
consists of motor neurons that innervate smooth muscle, cardiac muscle, and glands; it will make adjustments to ensure optimal support for body activities such as adjusting heart rate, blood pressure, and digestive processes; further breaks down in sympathetic or parasympathetic systems
afferent divison
aka sensory division; includes somatic and visceral sensory nerve fibres that conduct impulses from receptors to the CNS
2 types of nerve fibres in sensory divison
somatic sensory nerve fibres and visceral sensory nerve fibres
efferent division
aka motor division; motor nerve fibres that conduct impulses from the CNS to effectors (muscles and glands); breaks down into somatic and autonomic nervous systems
sympathetic division
mobilises body systems during activity; fight or flight system
parasympathetic system
conserves energy and promotes housekeeping functions during rest (rest and digest)
dual innervation
all visceral organs are served by autonomic divisions; however, they have opposite effects and this serves to maintain homeostasis
main differences between somatic and autonomic pathways
both have motor fibres but differ in their effectors, efferent pathways, ganglia, and target organ response to release neurotransmitters
main differences in muscle use or effectors between somatic and autonomic systems
somatic system uses skeletal muscle and is voluntary (except for reflexes), while the autonomic system is involved in smooth muscle, cardiac muscle, and glands, and is involuntary
efferent pathways in somatic nervous systems
has cell body in the CNS and is a single thick myelinated group A axon that extends in spinal or cranial nerves directly to skeletal muscle
autonomic nervous system efferent pathways
uses a two-neuron chain that is both preganglionic neuron and postganglionic neuron
differences in ganglia between somatic and autonomic systems
somatic ganglia are usually located in the dorsal root and autonomic ganglia are located close to the spinal cord (sympathetic) or in or near their visceral organ (parasympathetic)
preganglionic neuron
has the cell body in the CNS with thin, lightly myelinated axon extending to the ganglion
postganglionic neuron
outside the CNS and the cell body synapses with the preganglionic axon; its structure is unmyelinated and extends to the effector organ
somatic nervous system neurotransmitter effects
all neurons release acetylcholine, in which the effect is always stimulatory
autonomic nervous system neurotransmitter release
preganglionic fibres release acetylcholine and postganglionic fibres release acetylcholine or norepinephrine; the effect is either stimulatory or inhibitory, depending on the type of receptors
craniosacral divison
another name for parasympathetic division; called this because fibres originate from the brainstem and sacral regions of cord
thoracolumbar division
another name for the sympathetic division; called this because fibres originate in the thoracic and lumbar regions of the spinal cord
range for thoracolumbar division
T1-L2
length of fibres in sympathetic system
short preganglionic and long postganglionic fibres
length of fibres in parasympathetic system
long preganglionic and short postganglionic fibres
location of ganglia in parasympathetic system
located in or near their visceral effector organ
location of ganglia in sympathetic system
lie close to the spinal cord
site of origin for parasympathetic system
brain and sacral spinal cord; hence craniosacral
site of origin for sympathetic system
thoracic and lumbar regions; hence thoracolumbar
examples of effects of parasympathetic system
decreased blood pressure, heart rate, and respiratory rates, increased gastrointestinal activity, and constricted pupils
examples of effects of sympathetic system
increased blood pressure, heart rate, and respiratory rates, decreased gastrointestinal activity, and dilated pupils
visceral reflex
reflexes that involve an internal organ as the effector and have the same components as somatic reflexes but there are three main differences
examples of visceral reflexes
reflexes that empty the bladder and the rectum
similarities between reflex arcs and visceral reflexes
receptor, sensory neuron, integration centre, and effector
3 main differences between reflex arcs and visceral reflexes
visceral reflexes have two consecutive neurons in the motor pathway, the afferent fibres are visceral sensory neurons, and effectors are smooth muscle, cardiac muscle and glands rather than skeletal muscle
ventral ramus
one of the two primary branches that emerges from the spinal nerve (exits anterior); plays a crucial role in the distribution of motor and sensory innervation to the body’s anterior and lateral regions of the limbs
gray ramus communicans
branch of the sympathetic system that provides a route for unmyelinated, postganglionic fibres that connect the sympathetic trunk to the ventral ramus of a spinal nerve
white ramus communicans
branch of the sympathetic system that provides a route for myelinated preganglionic fibres that will synapse will the postganglionic neuron in the sympathetic trunk
sympathetic trunk
a chain of ganglia that extend from the base of the skull to the coccyx; is made of neuron cell bodies that lie outside the CNS and lie on either side of the vertebral column
what kind of peripheral nerves can you have?
cranial or spinal
how many pairs of mixed nerves are there in a spinal nerve?
31
what sensory fibres are apart of the sensory division?
somatic sensory fibres and visceral sensory fibres
what are different effects of the sympathetic and parasympathetic divisions caused by?
different neurotransmitters and receptor types of effectors
another name for interoreceptors
visceroreceptors
2 categories that sensory receptors belong to
simple receptors of the general senses and receptors for special senses
where are free nerve endings abundant?
epithelia and connective tissues
what are the most common receptors for encapsulated nerve endings?
mechanoreceptors
three ascending pathways for sensory information
dorsal column–medial lemniscal pathway, spinothalamic pathway, and spinocerebellar tract
2 other names for ANS
involuntary nervous system and general visceral motor system
similarities between somatic and autonomic systems
both are regulated by higher brain centres; both spinal and cranial nerves will contain somatic and autonomic fibres; and adaptations usually will involve both somatic and autonomic fibres
will parasympathetic or sympathetic system cause the liver to release glucose?
sympathetic
what system are white and grey communicantes part of?
the sympathetic system
what type of neurons are sensory neurons?
unipolar
what type of neurons are interneurons?
mulitpolar
what type of neurons are motor neurons?
multipolar
what first order neurons will vary greatly in shape and size?
encapsulated endings
three typical pathways of sympathetic innervation
synapse in trunk ganglion at the same level, at a higher or lower level, or pass through without synapsing here
synapse in trunk ganglion at the same level
the spinal nerve and ganglia are at the same level; the preganglionic neuron will travel through the ventral ramus and the white communicans where it will synapse with the postganglionic neuron in the sympathetic trunk ganglia, which will leave via the rami grey communicans and travel to the target effector
example of synapse in a trunk ganglion at the same level
T1 spinal nerve projects to T1 ganglia to innervate the trachea
synapse in trunk ganglion at a higher or lower level
the spinal nerve and ganglia are at different levels and this will occur when the target effector is below or above the thoracolumbar divison; the preganglionic neuron will synapse with the postganglionic neuron above or below
example of synapse in trunk ganglion at a higher or lower level
spinal nerve T1 needs to synapse with the eye so it will travel up through the sympathetic trunk until it reaches the cervical ganglion
passing through the trunk without synapsing
the preganglionic neuron will travel through additional branches of the ventral nerve (sphlanic) to the distal collateral ganglion where the synpase will occur
what is passing through the trunk without synapsing associated with?
controlling organs of the abdominal cavity
where will the synapse occur for passing through the trunk without synapsing?
distal collateral ganglion after travelling down the splanchnic nerve
what does mixed nerve mean?
nerves contain both sensory and motor fibres; sends impulses to and from the CNS
what system are cranial and spinal nerves part of?
the PNS
3 levels of sensory integration
receptor level, circuit level and perceptual level
EPSP
any stimulus that depolarises a membrane; excitatory postsynpatic potential
IPSP
any stimulus that hyperpolarises a membrane and inhibits action potentials; inhibitory postsynaptic
what is the gracile pathway used for and what is the cuneate pathway used for?
gracile for lower limbs and cuneate for upper limbs; these pathways are associated with light touch like tickling
posterior column medial leminscus pathway simple
FON will project up the spinal cord and synpase with SON in the cuneate or gracile nucelus of the medulla oblangata; the SON will then immediately decussates, passes thorugh the medial lemninscus in the midbrain and then synpase with the TON in the thalamus; TON will project to the primary somatosensory cortex
somatic motor direct pathway
UMN will synpase directly with LMN in the brain or spinal cord and the LMN will directly target an effector
2 corticospinal pathways
motor pathways; anterior and lateral
corticobulbar pathway
occurs when a cranial nerve is being used and is often movement in the face; an UMN will project through the cerebral peduncle in the pons or medulla where it decussates and synapses with a LMN that projects to a skeletal muscle
hormonal system of the sympathetic division
the preganglionic neuron can enter the adrenal medulla, releasing Ach and this triggers the release of chromaffin which triggers the release of epinephrine and norephinephinre into the bloodstream
what triggers the hormonal release of epinephrine and norepinephrine in the sympatheic resposne?
chromaffin
where in the thalamus does the second order neuron synapse with the third order neuron?
the ventral posterior nucleus
sacral outflow of nerves from parasympathetic divison
inferior hypogastric plexus and pelvic splanchnic nerve; both of these regulate the rectum, the bladder and ureters, and the genitalia
nerves associated with cranial outflow from parasympathetic division
oculomotor, facial, vagus, and glossopharyngeal nerves
oculomotor nerve cell body location for parasympathetic system
the ciliary ganglion
facial nerves cell body location for parasympathetic system
2 different branches (pteryogopalatine and submandibular ganglia)
glossopharyngeal nerve cell body location for parasympathetic system
otic ganglia
vagus nerve for parasympathetic system
has two main plexuses; cardiac/ pulmonary plexus will control heart rate and respiration, and the celiac plexus innervates the liver, gallbladder, and pancreas to secrete digestive enzymes
where are the splanic nerves located?
on the anterior side of the spinal cord
pathways to the head
include spinal nerves from T1-T4; these ascend to the superior cervical ganglia and control the head, eyes, and salivary glands
pathways to the thorax
include spinal nerves from T1-T6; these ascend to the middle cervical ganglia and combine into the cardiac and pulmonary plexus to control heart rate and the lungs
pathways to the collateral ganglia
the rest of the spinal nerves travel along the splanchnic nerves (greater, lesser, or lumbar) and travel to the celiac, superior mesenteric and inferior mesenteric ganglia
another name for a stimulus
generator potential
what kinds of receptors are all special senses associated with?
exteroreceptors
where is the medial lemniscus located?
in the midbrain
areas of synapse for PCML pathway
nuclei in the medulla (gracile or cuneate), thalamus, and primary somatosensory area in cerebral cortex
local circuit neurons
interpret the higher signals from the brain, focus them into a single signal that triggers the activation of the LMNs
where are local circuit neurons located?
brainstem and spinal cord
what are local circuit neurons important for?
coordination and gait
during the corticobulbar tract, where does a facial nerve synapse?
in the pons
during the corticobulbar tract, where does a hypoglossal nerve synapse?
in the medulla
2 nerves associated with the corticobulbar tract
the facial and hypoglossal nerve
what is chromaffin
a specialised neuron that will release neurotransmitters into the bloodstream
what are rami?
branches
does the sympathetic or parasympathetic system innervate more organs?
sympathetic
is the white or grey rami communication closer to the spinal cord?
grey
what do pathways to the head result in?
control skin and vessels of the head, dilate the eyes, inhibit salivary glands, and also increase heart rate
what do pathways to the thorax result in?
cardiac and pulmonary plexuses; increase breathing and heart rate
what does the oculomotor nerve do in the parasympathetic system?
innervates smooth muscle of the eye
what does the facial nerve do in the parasympathetic system?
controls crying and mucous production in the mouth and nose
what do the glossopharyngeal nerve do in the parasympathetic system?
activates the parotid salivary gland
what route do the majority of preganglionic nerves take in the sympathetic trunk?
passing through the trunk without synapsing
where are second order neurons located?
spinal cord or brainstem
what does the premotor area do?
plans and organises motor output
