Chapter 16: Lecture midterm II Flashcards
Sensation
conscious or subconscious awareness of changes in the external or internal environment
perception
conscious interpretation of sensation performed mainly by the cerebral cortex
General senses
- refer to both somatic and visceral senses
Somatic senses include:
- tactile sensations such as touch, pressure, vibration, itch and tickle, thermal sensations, pain sensations and proprioceptive sensations
Visceral senses
provide information about changes within internal organs; for example; pressure, stretch, chemical nausea, hunger, or temperature
Special senses:
include sensory modalities for smell, taste, vision, hearing and equilibrium or balance
What are the events that occur for sensation:
- stimulation of sensory receptor
- transduction of stimulus
- generation of nerve impulses
- integration of sensory input
What is stimulation of sensory receptor:
An appropriate stimulus must occur within the sensory receptors receptive field, that is, the body region where stimulation activates the receptor and produces a response
What is transduction of stimulus:
- a sensory receptor converts the energy in the stimulus to a graded potential
What is generation of nerve impulses
when a graded potential in a sensory neuron reaches threshold, and it triggers one or more nerve impulses which propagate towards the CNS
Sensory neurons that conduct nerve impulses from the PNS to CNS are known as…
first-order neurons
What is integration of sensory input
- a particular region of the CNS recieves and integrate (processes) the sensory nerve impulse
- conscious sensations or perceptions are integrated in the cerebral cortex
free nerve endings:
- bare dendrites associated with pain, thermal, itch, tickle and some touch sensations
encapsulated nerve endings
- dendrites enclosed in connective tissue capsule for pressure, vibration and some touch sensations
separate cells:
receptor cells that synapse with first-order sensory neurons; located in the retina, inner ear or taste buds
exteroceptors
- located at or near the surface of the body; sensitive to stimuli coming from outside of the body
- conveys: visual, smell, taste, touch, pressure, vibration, thermal and pain sensations
interoceptors
- located in blood vessels, visceral organs, and nervous system; provide information about internal environment
- impulses are usually not consciously perceived but may be felt as pressure or pain
proprioceptors
located in muscles, tendons, joints and inner ear; provide information about body position an motion of joints and equilibrium
mechanoreceptors
detect mechanical stimuli: provide sensations of touch, pressure, vibration, proprioception and hearing and equilibrium
thermoreceptors
detect changes in temp
nociceptors
respond to painful stimuli
photoreceptors
detect light that strikes the retina of the eye
chemoreceptors
detect chemicals in mouth (taste), nose (smell) and body fluids
osmoreceptors
sense osmotic pressure of body fluids
areas with highest density of somatic sensory receptors are;
- tip of the tongue
- lips
- fingertips
What are the four modalities for somatic sensations
- tactile
- thermal
- pain
- proprioceptive
Deep somatic pain:
skeletal muscles, joints, tendons and fascia
Visceral pain:
stimulation of pain sensory in visceral organs
- usually presents in or just deep into the skin that overlies the stimulates organ
Muscle spindles:
- type of proprioceptor found in skeletal muscles, that monitors muscle length and are involved in some stretch reflexes
Tendon organs
- type of proprioceptor found at the junction of a tendon and a muscle
- protects muscles and tendons from damage due to overstretching
Joint kinesthetic receptors
- exist in and around the joint capsule of synovial joints and they respond to pressure, acceleration, deceleration during movement to help protect against excessive strain
What are the different tactile receptors:
- tactile corpuscles
- hair root plexus
- non-encapsulated sensory corpuscles
- bulbous corpuscle
- lamellar corpuscle
- itch and tickle receptors
Tactile corpuscles:
- capsule surrounds mass of modified schwann cels and nerve endings in dermal papillae of hairless skin
- sensations: onset of touch and low frequency vibrations
Hair root plexus:
- free nerve endings wrapped around hair follicles in skin
- sensations: movements on skin surface that disturb hairs
Non- encapsulated sensory corpuscles:
- saucer-shaped free nerve endings make contact with tactile epithelial cells in dermis
- sensations: continuous touch and pressure
Bulbous corpuscles:
- elongated capsule surrounds nerve endings and schwann cells deep in dermis and ligaments and tendons
- Sensations: skin stretching and pressure
Lamellar corpuscles:
- oval, layered capsule surrounds nerve endings; present in dermis and subcutaneous tissue, submucosal tissues, joints, periosteum, and some viscera
- Sensations: high frequency vibrations
Itch and tickle receptors:
- free nerve endings in skin and mucous membranes
- Sensations: itch and tickle
somatosensory pathways relay information from somatic sensory receptors in the skin, muscles and joints to the …
primary somatosensory cortex
where is the primary somatosensory cortex located
(postcentral gyrus) in the parietal lobe of the cerebrum and the cerebellum
first - order (primary) neurons
- conduct nerve impulses from somatic sensory receptors into the brainstem or spinal cord
second - order (secondary) neurons
- conduct nerve impulses from the brainstem or spinal cord to the thalamus
- axons of second order neurons decussate as they course through the brainstem or spinal cord before ascending to the thalamus
third - order (tertiary) neurons
- conduct nerve impulses from the thalamus to the primary somatosensory cortex on the same side
- as the impulses reach the primary somatosensory cortex, perception of the sensation occurs
Posterior column-medial lemniscus pathway conveys impulses from the
limbs, trunk, neck and posterior head
Posterior column-medial lemniscus’s first order neurons extend from peripheral sensory receptors to the…
spinal cord
Once the Posterior column-medial lemniscus pathway’s first-order neurons have entered the spinal cord they..
ascend to the medulla via tracts known as the posterior columns
the first-order neurons of the Posterior column-medial lemniscus pathway synapse with second order neurons at the…
medulla
Axons of the second-order neurons of the Posterior column-medial lemniscus pathway decussate at the —— and enter the
the medulla, the medial lemniscus
what is the medial lemniscus
thin ribbon like projection that extends from the medulla to the thalamus
Once the second-order neurons synapse with third order neurons from the Posterior column-medial lemniscus pathway at the —–, they project the sensations to the
thalamus, primary somatosensory cortex of the cerebrum
The anterolateral (spinothalamic) pathway conveys nerve impulses for
pain, touch, pressure and temp
first order neurons of the anterolateral (spinothalamic) pathway synapse with second order neurons at the…
posterior gray horns of the spinal cord on the same side of the body
the second order neurons of the anterolateral (spinothalamic) pathway decussate at the —- and then ascend to
spinal cord and then ascend via the spinothalamic tract
the second-order neurons synapse with the third-order neurons at the
thalamus and the third-order neurons convey the impulses to the primary somatosensory cortex
The trigeminothalamic pathway convey nerve impulses
for pain, temperature, touch and proprioception from the face, nasal cavity, oral cavity, and teeth ascend into the cerebral cortex along the trigeminothalamic pathway
first-order neurons of the trigeminothalamic pathway extend from sensory receptors in the face, nasal cavity, and teeth into the….
pons through the trigeminal (V) nerves
the cell bodies of the first order neurons for the trigeminothalamic pathway are in the …
trigeminal ganglion
the axon terminals of some first order neurons in the trigeminothalamic pathway synapse in —- while others synapse in —-
the pons, the medulla
the axons of the second-order neurons in the trigeminothalamic pathway cross to the opposite side of the pons and medulla and ascend as the ….
trigeminothalamic tract to the thalamus
in the thalamus the axons terminals of the second order neurons synapse with the third order neurons of the trigeminothalamic pathway and go straight to the
primary somatosensory cortex on the same side of the cerebral cortex as the thalamus
anterior and posterior spinocerebellar pathways convey nerve impulses from
proprioceptors of one side of the body to the same side of cerebellum
anterior and posterior spinocerebellar pathways allow the
coordination of smooth and refine skills movement and maintain posture and balance
nerves that extend out of the brain stem and spinal cord are called
lower motor neurons
LMNs innervate skeletal muscles of the
face and head through cranial nerves and skeletal muscles of the limbs and trunk through spinal nerves
LMNs are divided into 4 distinct circuits:
- local circuit neurons
- upper motor neurons
- corpus striatum neurons
- cerebellar neurons
Local circuit neurons:
- located close to the lower motor neuron cell bodies in the brain stem and spinal cord
- receive input from somatic sensory receptors such as nociceptors, and muscle centers in the brain
- they help coordinate rhythmic activity in specific muscle groups, such as alternating flexion and extension of lower limbs when walking
Both local motor neurons and lower motor neurons receive input from
upper motor neurons
upper motor neurons
- have cell bodies in motor processing centers in upper parts of the CNS
- essential for the planning and execution of voluntary movements of the body
- originate in motor centers of the brain stem: vestibular nuclei, reticular formation, superio colliculus, red nucleus
most upper motor neurons synapse with
local circuit neurons, which then synapse with lower motor neurons
- some synapse directly with lower motor neurons
corpus striatum neurons
- assist movement by providing input to upper motor neurons
- neural circuits interconnect with corpus striatum nuclei with motor areas of the cerebral cortex (via the thalamus) and the brainstem
Corpus striatum neurons help to
initiate and terminate movements, supress unwanted movement, and establish and establish a normal level of muscle tone
Cerebellar neurons
- aid movement by controlling the activity of upper motor neurons
- a prime function of the cerebellum is to monitor differences between intended movements and movements actually performed
upper motor neurons extend to lower motor neurons via two pathways
direct and indirect motor pathways
Direct motor neurons provide input to lower motor neurons via axons that extend
directly from the primary somatosensory cortex
nerve impulses fro voluntary movements propagate from the primary motor cortex via
direct motor pathways
direct motor neurons consist of axons that descend from the
pyramidal cells of the primary cortex
direct motor pathways consist of
corticospinal pathways, and corticobulbar pathways
the corticospinal includes:
lateral corticospinal and anterior corticospinal pathways
Lateral corticospinal pathways conveys nerve impulses from the primary motor cortex to
skeletal muscles on the opposite side of the body for prescise, voluntary movements of distal parts of limbs
axons from lateral corticospinal pathways descend down to the
medulla and 90% decussate and enter the contralateral side of the spinal cord to form this tract
at their level of termination UMNs from the lateral corticospinal pathways end in
anterior gray horns on the same side and provide input to LMNs which innervates skeletal muscles
anterior corticospinal pathways conveys nerve impulses from
primary motor cortex to skeletal muscles on the opposite side of the body for movements of trunk and proximal part of limbs
axons of the UMNs in the anterior corticospinal pathways descend down to the
medulla and the 10% that do not decussate, enter th spinal cord to form this tract
at their level of termination, UMNS of the anterior corticospinal pathways descussate and end in
anterior gray horn on the opposite side of the body and provide input to LMNs which innervate skeletal muscles
corticobulbar pathways convey nerve impulses from the
primary motor cortex to skeletal muscles of the head to coordinate precise voluntary movements
axons of UMNs of corticobulbar pathways descend from the cortex to the
brainstem where some decussate and others do not
UMNs of corticobulbar pathways provide input to LMNs of
oculomotor (III), trochlear (IV), trigeminal (V), abducens (VI), facial (VII), glossopharyngeal (IX), vagus (X), and acessory (XI) and hypoglossal (XII) nerves, which control voluntary movements of the eyes, tongue, and neck
Indirect motor pathways deliver signals to LMNs from motor centers in
basal nuclei, cerebellum, and cerebral cortex
In indirect pathways axons of UMNs descend from the brainstem motor centers to five major tracts
- rubrospinal
- tectospinal
- vestibulospinal
- lateral reticulospiinal,
- medial reticulospinal tracts
in general indirect motor pathways convey nerve impulses from the brainstem to cause
involuntary movements that regulate posture, balance, muscle tone, and reflexive movements of the head and trunk
Rubrospinal pathways (indirect)
- conveys impulses from red nucleus to contralateral skeletal muscles that govern precise voluntary movements of distal parts of limbs
Tectospinal pathways (indirect)
- conveys nerve impulses from superior colliculus to contralateral muscles that reflexively move head, eyes, and trunk in response to visual or auditory stimuli
Vestibulospinal pathways
- conveys nerve impulses from vestibular nucleus (recieves input from head movements from inner ear) to ipsilateral skeletal muscles of trunk and proximal parts of limbs for maintaining posture and balance in response to head movements
Lateral and medial reticulospinal pathways
- conveys nerve impulses from reticular formation to ipsilateral skeletal muscles of trunk and proximal parts of limbs for maintaining posture and regulating muscle tone in response to ongoing body movements
4 functions of cerebellum
- monitoring intentions for movements
- monitoring actual movements
- comparing command signals with sensory information
- sending out corrective feedback
humans sleep and awaken in a 24-cycle called
circadian rhythm
our bodies rely on the reticular activating system to
stimulate the cerebral cortex
when the RAS is active
many nerve impulses are transmitted to widespread areas of the cerebral cortex, both directly via the thalamus
What can activate the RAS
- painful stimuli detected by nociceptors
- touch and pressure on the skin
- movement of the limbs
- bright light or the buzz of an alarm clock
Once the RAS is activated the cerebral cortex is also activated which causes
arousal
No amount of strong odours can cause
arousal
sleep
a state of altered consciousness or partial unconsciousness from which an individual can be aroused
coma
a state of unconscious in which an individual has little or no response to stimuli
causes of comas include
head injuries, damages to RAS, brain infections, overdoses
after a few weeks of coma patients can enter a
vegetative state
A normal sleep consists of two components;
NREM and REM sleep
How many stages of the NREM cycle
4
Stage 1 of NREM cycle:
- transition stage from awake to sleep (1-7 min)
- fleeting thoughts
- people who are awakened in this stage often say they have not been sleeping
Stage 2 of NREM cycle:
- also called light sleep (first stage of true sleep)
- a person is easy to awaken
- fragments of dreams may appear and eyes may roll slightly from side to side
Stage 3 of NREM cycle:
- a period of moderately deep sleep
- body temp and bp decrease and it is more difficult to waken the person
- this stage occurs about 20 min after falling asleep
Stage 4 of NREM cycle:
- deepest level of sleep
- although brain metabolism decreases significantly, body temp drops slightly, most reflexes are intact and muscle tone is decreased only slightly
- very difficult to wake the person up in this stage
REM sleep aka paradoxical sleep
- neuronal activity is high during REM sleep
- eyes move rapidly under closed eyelids
when dreams occur in NREM sleep, the dreams are usually less vivid and less emotional than
REM dreams. plus NREM dreams are more logical
Memory is the process by which
information acquired through learning is stored and retrieved
What are the two types of memory
declarative and procedural memory
Declarative memory:
memory than can be verbalized such as facts, events, objects, and names
Declarative memory requires
conscious recall
Procedural memory:
memory of motor skills, procedures and rules
example: riding a bike
Memory consolidation
process by which short term memory is converted into long term memory
Wernicke’s association area
- certain smells remind you of something
- cultural influence
- gives meaning by associating
Parkinsons disease affects people around age
60
Parkinsons disease occurs when
too little dopamine is produced by the substantia nigra
S&S of parkinsons
- shuffling gait
- tremor
- bradykinesia
- hypokinesia (pill -rolling)
Cerebral palsy
a motor disorder that results in the loss of muscle control and coordination; caused by damage to motor areas of the brain during fetal life, birth or infancy
Radiation during fetal life, temporary lack of oxygen, and hydrocephalus during infancy may cause
cerebral palsy
