Chapter 16: Sensory, Motor and Integrative Systems Flashcards
What is sensation?
Conscious or subconscious awareness of changes in the internal or external environment.
What is perception?
Conscious interpretation of sensations.
Sensory modality.
Each type of sensation.
A given sensory neuron carries information for how many sensory modalities?
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General senses.
Somatic senses and visceral senses.
Special senses.
Smell, taste, vision, hearing, equilibrium.
Somatic senses.
Tactile, thermal, pain, proprioception.
Visceral senses.
Pressure, stretch, chemicals, nausea, hunger, temperature of internal organs.
Does a sensory receptor respond to stimuli of other sensory modalities?
Weakly or not at all.
Where are conscious sensations or perceptions integrated?
Cerebral cortex.
Free nerve endings of first-order sensory neurons.
Bare dendrites, not encapsulated, lack any structural specializations. Attached to small diameter unmyelinated C-fibres.
What sensations are sensed by free nerve endings?
Pain, temperature, tickle, itch, touch.
Encapsulated nerve endings of first-order sensory neurons.
Dendrites are enclosed in a connective tissue capsule, distinctive microscopic structure, different types of capsules enhance the sensitivity or specificity of the receptor. Attached to large diameter myelinated A-fibres.
What sensations are sensed by encapsulated nerve endings?
Pressure, vibration, touch.
Separate cells that synapse with first-order sensory neurons.
Hair cells for hearing and equilibrium. Gustatory receptors on tastebuds. Photoreceptors in retina. Receptor potential triggers release of NT –> PSP in sensory neuron –> triggers nerve impulses if threshold is reached.
Exteroceptors.
At or near the external surface of the body. Sensitive to stimuli originating outside the body. Provide information about external environment.
What sensations are sensed by exteroceptors?
Hearing, vision, smell, taste, touch, pressure, vibration, temperature, pain.
Interoceptors.
Visceroceptors in blood vessels, visceral organs, muscles and nervous system. Provide information about internal environment. Not consciously perceived. Activation by strong stimuli may be felt as pain or pressure.
Proprioceptors.
In muscles, tendons, joints and inner ear. Provide information about body position, muscle length, muscle tension, and position and movement of joints.
Mechanoreceptors.
Detect stretching and bending of cells, as well as touch, pressure, vibration, proprioception, hearing, equilibrium.
Chemoreceptors.
Detect chemicals in mouth, nose and body fluids.
Osmoreceptors.
Detect osmotic pressure of body fluids.
Describe adaptation in sensory receptors.
Receptor potential decreases in amplitude during a maintained constant stimulus which causes the frequency of the nerve impulse to decrease. This causes the perception of a sensation to fade or disappear even though the stimulus persists.
Rapidly adapting receptors.
Adapt very quickly as they are specialized for signalling changes in a stimulus.
Slowly adapting receptors.
Adapt slowly and continue to trigger nerve impulses as long as the stimulus persists.
What sensations are sensed by rapidly adapting receptors?
Vibration, touch, smell.
What sensations are sensed by slowly adapting receptors?
Pain, body position, chemical composition of blood.
Somatic sensations arise from stimulation of sensory receptors in what locations?
Skin, subcutaneous layer, skeletal muscles, tendons, joints, mucous membranes of the mouth, vagina and anus.
Where is there a high density of somatic sensory receptors?
Tip of tongue, lips, and fingertips.
Tactile sensations.
Touch, pressure, vibration, itch, tickle.
Touch.
Stimulation of tactile receptors in the skin or subcutaneous layer.
Which receptors sense touch?
Corpuscles of touch, hair root plexuses, type I cutaneous mechanoreceptors, type II cutaneous mechanoreceptors.
Corpuscles of touch.
Meissner corpuscles. Rapidly adapting.
Where are corpuscles of touch located?
In dermal papillae of hairless skin: fingertips, hands, eyelids, top of tongue, lips, nipples, soles, clitoris, tip of penis.
Hair root plexuses.
Rapidly adapting. Free nerve endings are wrapped around hair follicles. Detect movements on skin surface that disturb hairs. Located in hairy skin.
Type I cutaneous mechanoreceptor.
Tactile Merkel disc. Slowly adapting. Flattened free nerve endings make contact with tactile epithelial cells of stratum basale. Located in fingertips, hands, lips, external genitalia.
Type II cutaneous mechanoreceptor.
Ruffini corpuscle. Slowly adapting. Elongated encapsulated nerve endings. Located in dermis and subcutaneous layer.
What are type II cutaneous mechanoreceptors sensitive to?
Skin stretching.
Pressure.
Sustained sensation that is felt over a large area. Occurs with deep deformation of the skin and subcutaneous layer.
Which receptors sense pressure?
Type I and II mechanoreceptors.
Vibration.
Rapidly repetitive sensory signals from tactile receptors.
Which receptors sense vibration?
Lamellated corpuscles and corpuscles of touch.
Lamellated corpuscles.
Pacinian corpuscles. Rapidly adapting. Located in dermis and subcutaneous layer.
What are lamellated corpuscles sensitive to?
High frequency vibrations.
What are corpuscles of touch sensitive to?
Low frequency vibrations.
Itch.
Stimulation of free nerve endings by certain chemicals or antigens.
Why does scratching alleviate itching?
Activates a pathway that blocks transmission of the itch signal through the spinal cord.
Tickle.
Stimulates free nerve endings.
Which receptors detect thermal sensations?
Thermoreceptors, which are free nerve endings that have receptive fields about 1mm in diameter on the skin surface. They continue to generate impulses at a lower frequency throughout a prolonged stimulus.
Which temperatures stimulate pain receptors?
Under 10 C. Over 45 C.
Cold receptors.
Rapidly adapting. Located in stratum basale of epidermis. Attaches to medium diameter myelinated A-fibres. A few connect to small diameter unmyelinated C-fibres. Detect temperatures 10-35 C.
Warm receptors.
Rapidly adapting. Located in dermis. Attached to small diameter unmyelinated C-fibres. Less abundant than cold receptors. Detect temperatures 30-45 C.
Which receptors detect pain sensations?
Nociceptors, which are free nerve endings found in every tissue of the body except the brain. Stimulated by intense thermal, mechanical or chemical stimuli.
Why would nociceptors detect chemicals?
Tissue irritation and injury can release chemicals and K+.
Why would pain persist after the stimuli is removed?
Pain-mediating chemicals linger, and nociceptors exhibit very little adaptation.
Fast pain.
Occurs within 0.1 seconds after the stimulus. Detected by nociceptors attached to medium diameter myelinated A-fibres. Not felt in deeper tissues of the body. Examples: acute, sharp, pricking.
Slow pain.
Occurs within a second or more after the stimulus, and gradually increases in intensity. Detected by nociceptors attached to small diameter unmyelinated C-fibres. Can occur in the skin and in deeper tissues. Examples: burning, chronic, aching, throbbing.
Superficial somatic pain.
Arises from stimulation of receptors in the skin.
Deep somatic pain.
Arises from stimulation of receptors in skeletal muscles, joints, tendons, fascia.
Visceral pain.
Arises from stimulation of nociceptors in visceral organs.
Referred pain.
Pain is felt in a surface area far from the stimulated organ. The visceral organ and area of pain are served by the same segment of the spinal cord.
Kinesthesia.
Perception of body movements.
Which receptors sense proprioceptive sensations?
Proprioceptors, muscle spindles, tendon organs, joint kinesthetic receptors.
Proprioceptors.
Slowly adapting. The brain continually receives impulses related to proprioception. Allow for weight discrimination of objects and tasks.
Muscle spindles.
Slowly adapting. Nerve endings wrap around 3-10 intrafusal fibres. Detect changes in skeletal muscle length. Involved in stretch reflexes.
Where are there an abundance of muscle spindles?
Areas that produce finely controlled movements.
Which muscles lack muscle spindles?
In middle ear.
Gamma motor neurons.
Adjust tension in muscle spindles.
Tendon organs.
Slowly adapting. Located in the junction of a tendon and a muscle. Protect tendons and associated muscles from damage and excessive tension.
Joint kinesthetic receptors.
Type II cutaneous mechanoreceptors. Located within and around articular capsules of synovial joints. Respond to pressure.
Where do somatic sensory pathways relay information to?
Somatic sensory receptors –> primary somatosensory area and cerebellum.
Impulses propagate from which areas along cranial nerves into the brainstem?
Face, nasal cavity, oral cavity, teeth, eyes.
Impulses propagate from which areas along spinal nerves into the spinal cord?
Neck, trunk, limbs, posterior head.
Where do second order neurons of somatic sensory pathways conduct impulses to?
Thalamus after decussation.
Where do third order neurons of somatic sensory pathways conduct impulses to?
Primary somatosensory area on the same side.
Posterior column-medial lemniscus pathway (PCML).
Propagates impulses of touch, pressure, vibration, proprioception from limbs, trunk, neck, and posterior head.
Where are the cell bodies of the first order neurons of the PCML located?
Dorsal root ganglia of spinal nerves.
Where are the dendrites of the second order neurons of the PCML located?
Gracile nucleus or cuneate nucleus of medulla oblongata.
Impulses for touch, pressure, vibration and conscious proprioception from upper limbs, upper trunk, neck and posterior head propagate along:
Axons in cuneate fasciculus –> cuneate nucleus.
Impulses for touch, pressure, vibration and conscious proprioception from lower limbs and lower trunk propagate along:
Axons in gracile fasciculus –> gracile nucleus.
Describe the propagation of impulses along the PCML.
First order neurons –> medulla oblongata –> second order neurons –> decussation in medulla –> medial lemniscus –> thalamus –> third order neurons –> primary somatosensory area.
Anterolateral pathway (spinothalamic).
Propagates impulses of pain, temperature, itch, tickle from limbs, trunk, neck and posterior head.
Where are the cell bodies of the first order neurons of the anterolateral pathway?
Posterior root ganglia.
Where are the cell bodies of the second order neurons of the anterolateral pathway?
Posterior gray horn of spinal cord.
Describe the propagation of impulses along the anterolateral pathway.
First order neurons –> posterior gray horn of spinal cord –> second order neurons –> decussation in spinal cord –> ventral posterior nucleus of thalamus –> third order neurons –> primary somatosensory area.
Trigeminothalamic pathway.
Propagates impulses of somatic sensations from face, nasal cavity, oral cavity and teeth.
Where are the cell bodies of the first order neurons of the trigeminothalamic pathway?
Trigeminal ganglia.
Describe the propagation of impulses through the trigeminothalamic pathway?
First order neurons –> pons through trigeminal nerves –> or medulla –> second order neurons –> decussation in pons or medulla –> ventral posterior nucleus of thalamus –> third order neurons –> primary somatosensory area.
Somatic sensory map and somatic motor map.
Relate body parts to cortical areas.
Where is the primary somatosensory area?
Postcentral gyri of parietal lobes of cerebral cortex.
Localization of somatic sensations occurs when:
Nerve impulses arrive at the primary somatosensory area.
What are the two somatic sensory pathways to the cerebellum?
Anterior spinocerebellar tract and posterior spinocerebellar tract.
What somatic senses propagate to the cerebellum?
Posture, balance, coordination of skilled movements. Not consciously perceived. Ipsilateral.
What structures orchestrate all voluntary movements?
Neural circuits in brain and spinal cord.
Lower motor neurons extend from brainstem axons through:
Cranial nerves to innervate skeletal muscles of face and head.
Lower motor neurons extend from spinal cord axons through:
Spinal nerves to innervate skeletal muscles of limbs and trunk.
Input arrives at lower motor neurons from:
Local circuit neurons, which are located close to the cell bodies of the lower motor neurons, and work to coordinate rhythmic activity in specific muscle groups.
Upper motor neurons that control body movements.
Are actually interneurons that relay impulses to local circuit neurons and LMNs. Cell bodies are in motor processing centres in upper parts of the CNS.
Upper motor neurons from the cerebral cortex are essential for:
Planning and executing voluntary movements.
Upper motor neurons from the brainstem are essential for:
Posture, balance, muscle tone, and reflexive movements of the head and trunk.
Basal nuclei neurons.
Assist movement by providing input to UMNs. Neural circuits interconnect the basal nuclei with motor areas of the cerebral cortex and brainstem, and these circuits help initiate and terminate movements, suppress unwanted movements, and establish a normal level of muscle tone.
Cerebellar neurons.
Assist movement by controlling the activity of UMNs. Neural circuits interconnect the cerebellum with motor areas of the cerebral cortex and brainstem. Monitor difference between intended and actual movements. Issue commands to UMNs to reduce movement errors. Coordinates body movements. Maintains posture and balance.
Premotor area.
Area 6. Develops the motor plan after the desire to move a body part is sent to basal nuclei and thalamus. Identifies which muscles should contract. Identifies how much muscles need to contract. Identifies in what order the muscles need to contract. Stores information about learned motor activities. The plan is transmitted to the primary motor area for execution.
Primary motor area.
Area 4. Major control region for the execution of voluntary movements.
Electrical stimulation of any point of the primary motor area causes:
Contraction of specific muscles on the opposite side of the body.
How does the primary motor area control movements?
Forms descending pathways that extend to the spinal cord and brainstem. The pathways are the corticospinal pathways and the corticobulbar pathway.
Direct motor pathways.
Pyramidal pathways, since axons descend from pyramidal cells (UMNs) of primary motor area and premotor area to LMNs. Control voluntary movements.
What are the two corticospinal pathways?
Lateral corticospinal tract and anterior corticospinal tract.
Corticospinal pathways.
Conduct impulses for the control of muscles of the limbs and trunk. Axons of UMNs descend through internal capsule and cerebral peduncles to form pyramids. 90% decussate.
Lateral corticospinal tract.
Contain the axons that decussate in the medulla oblongata. Located in lateral white column of spinal cord. Axons of UMNs synapse with local circuit neurons or LMNs in anterior gray horn of spinal cord. Axons of LMNs exit the spinal cord in anterior roots of spinal nerves and terminate in skeletal muscles that control movements of distal limbs. Involved in the precise highly skilled movements of hands and feet.
Anterior corticospinal tract.
Contain the axons that do not decussate in the medulla oblongata. Located in anterior white column of spinal cord. At each spinal cord level, some of these axons decussate via the anterior white commissure. Axons of UMNs synapse with local circuit neurons or LMNs in anterior gray horn of spinal cord. Axons of LMNs exit the spinal cord in anterior roots of spinal nerves and terminate in skeletal muscles that control movements of trunk and proximal limbs.
Corticobulbar pathway.
Conducts impulses to control skeletal muscles in head. Axons of LMNs terminate in the motor nuclei of 9 cranial nerves in the brainstem. Involved in precise voluntary movements of eye, tongue, neck, chewing, facial expressions, speech, swallowing.
What are the 9 cranial nerves involved in the corticobulbar pathway?
Oculomotor, trochlea, trigeminal, abducens, facial, glossopharyngeal, vagus, accessory, hypoglossal.
Indirect motor pathways.
Extrapyramidal pathways. Include all somatic motor tracts other than the corticospinal and corticobulbar tracts. Provide input to LMNs from motor centres in the brainstem. Cause involuntary movements that regulate posture, balance, muscle tone, and reflexive movements of the head and trunk.
What are the 5 indirect motor pathways?
Rubrospinal tract, tectospinal tract, vestibulospinal tract, lateral reticulospinal tract, and medial reticulospinal tract.
Which indirect motor tract is involved with voluntary movements?
Rubrospinal tract, which regulates movements of the upper limbs alongside the lateral corticospinal tract.
Vestibular nuclei.
Located in the medulla and pons. Maintain posture in response to changes in equilibrium.
What 3 sources provide input to the vestibular nuclei?
1) Eyes: provide visual information about body position. 2) Vestibular apparatus of inner ear: provides information about head position. 3) Proprioceptors in muscles and joints: provide information about limb position.
Which nerve and brain structure send input to the vestibular nuclei?
Vestibulocochlear nerve and cerebellum.
Which indirect motor tract receives input from the vestibular nuclei regarding skeletal muscles of the trunk and proximal limbs?
Vestibulospinal tract.
Reticular formation.
Receives input from eyes, ears, cerebellum and basal nuclei. Generates APs along medial and lateral reticulospinal tracts to skeletal muscles of the trunk and proximal limbs. Works to maintain posture and regulate muscle tone.
What is the main difference between the medial and lateral reticulospinal tracts?
Medial: excites skeletal muscles. Lateral: inhibits skeletal muscles.
Superior colliculus.
Receives visual input from eyes and auditory input from ears. When input occurs in a sudden and unexpected manner, the superior colliculus produces APs along the tectospinal tract to activate skeletal muscles in the head and trunk.
Which structure is the integrating centre for saccades?
Superior colliculus.
Describe the UMNs, local circuit neurons and LMNs of the superior colliculus?
UMNs synapse with local circuit neurons in the gaze centres of reticular formation –> local circuit neurons synapse with LMNs in nuclei of oculomotor, trochlear and abducens nerves.
Red nucleus.
Receives input from cerebral cortex and cerebellum. Generates APs along the axons of the rubrospinal tract to activate skeletal muscles of the distal upper limbs for fine voluntary movements.
What is not activated by the rubrospinal tract?
Distal lower limbs.
What are the 4 functions of the basal nuclei?
1) Initiate movements. 2) Suppress unwanted movements. 3) Regulate muscle tone. 4) Regulate non-motor processes.
How do the basal nuclei initiate movements?
Basal nuclei neurons receive input from sensory, association and motor areas of the cerebral cortex. Output is sent to thalamus –> premotor area –> UMNs in primary motor area –> activate corticospinal and vcortciobulbar tracts to promote movement.
How do the basal nuclei suppress unwanted movements?
They tonically inhibit the neurons of the thalamus that affect the activity of the UMNs in the motor cortex.
How do the basal nuclei regulate muscle tone?
They send APs to reticular formation to reduce muscle tone via medial and lateral reticulospinal tracts.
How do the basal nuclei regulate non-motor processes?
They influence sensory, limbic, cognitive and linguistic functions.
How does the cerebellum maintain proper posture and balance?
Monitors intentions for movement, monitors actual movement, compares command signals with sensory information, and sends out corrective feedback.
How does the cerebellum monitor intentions for movement?
Cerebellum receives impulses from motor cortex and basal nuclei via the pontine nuclei regarding what movements are planned.
How does the cerebellum monitor actual movement?
Cerebellum receives input from proprioceptors in joints and muscles that reveal what is actually happening. The nerve impulses travel in the anterior and posterior spinocerebellar tracts.
How does the cerebellum send out correct feedback?
If there is a discrepancy between intended and actual movement, the cerebellum sends feedback to the UMNs in the cerebral cortex via the thalamus, and then to the UMNs in brainstem motor centres to provide error corrections.
What integrative functions are the responsibility of the cerebrum?
Wakefulness, sleep, learning, memory and language.
What structure in the hypothalamus establishes the circadian rhythm?
Suprachiasmatic nucleus.
Sleep.
State of altered consciousness and partial unconsciousness from which an individual can be aroused.
What are the stages of sleep, and how does a person cycle through them?
NREM 1 –> NREM 2 –> NREM 3 –> NREM 4 –> NREM 3 –> NREM 2 –> NREM 1 –> REM
NREM stage 1.
Transition between wakefulness and sleep. Lasts 1-7 minutes.
NREM stage 2.
Light sleep, first stage of true sleep, easily awakened, fragments of dreams, eyes slowly roll from side to side.
NREM stage 3.
Moderately deep sleep, temperature decreases, BP decreases, 20 minutes after falling asleep.
NREM stage 4.
Deepest level of sleep, brain metabolism decreases, temperature drops more, most reflexes remain intact, muscle tone is decreased.
REM.
Most dreaming occurs here, eyes move rapidly from side to side, paradoxical sleep, high frequency small amplitude waves in ECG (similar to wakefulness), increased HR, increased RR, increased BP, inhibition of somatic neurons, decreased muscle tone, paralyzed skeletal muscles. More emotional, vivid and less logical dreams occur during this stage. Brain blood flow and oxygen use are higher during REM than intense mental or physical activity.
How long is the REM stage of sleep?
The first REM lasts 10-20 minutes, and then gradually increases with the final REM lasting 50 minutes. REM sleep totals 90-120 minutes during an 8 hour period of sleep.
How is NREM sleep induced?
By NREM sleep centres in the hypothalamus and basal forebrain.
How is REM sleep induced?
By REM sleep centres in the pons and midbrain.
RAS activity is low during sleep due to which inhibitory chemical?
Adenosine.
Adenosine.
Accumulates during periods of high ATP usage by the nervous system, and inhibits neurons of RAS that participate in arousal by binding to A1 receptors.
How do caffeine and theophylline (tea) maintain wakefulness?
Block A1 receptors, preventing adenosine from binding and inducing sleep.
Functions of sleep.
Restoration, memory consolidation, immune system enhancement, brain maturation.
Coma.
State of unconsciousness in which an individual has little or no response to stimuli.
What can result in a coma?
Head injuries, RAS damage, brain infections, alcohol intoxications, drug overdoses.
What does absence of brain waves in ECG indicate?
Brain dead.
Persistent vegetative state.
A few weeks in a coma. Patient has normal sleep-wake cycles, but no awareness of surroundings, unable to speak, unable to respond to commands. Patients smile, laugh and cry but do not understand the meanings of these actions.
Associative learning.
Occurs when a connection is made between two stimuli. Otherwise known as classical conditioning.
Nonassociative learning.
Occurs when repeated exposure to a single stimulus causes a change in behaviour. Habituation: repeated exposure to irrelevant stimulus = decreased response. Sensitization: repeated exposure to noxious stimulus = increased response.
Declarative/explicit memory.
Memory of experience that can be verbalized. Requires conscious recall. Stored in association areas of cerebral cortex.
Procedural/implicit memory.
Memory of motor skills. Does not require conscious recall. Stored in basal nuclei, cerebellum, premotor area.
Memory consolidation.
Process of short-term memory transforming into long-term memory. Major role for hippocampus.
What contributes to consolidation?
Repetition.
Long term potentiation.
Transmission at some synapses within the hippocampus is enhanced for hours or weeks after a brief period of high frequency stimulation.
Where are language areas in the brain?
Left hemisphere.
Wernicke’s area.
Association area in temporal lobe. Interprets meaning of written and spoken words, translates words into thoughts, and receives input from primary visual area and primary auditory area.
Broca’s area.
Motor area in frontal lobe. Translates thoughts into words, receives input from Wernicke’s area, generates a motor pattern for activation of muscles needed to speak, sends motor pattern to primary motor area, and activates appropriate speech muscles.
