Chapter 16 Flashcards
Sensation
Is the conscious or subconscious awareness of changes in the external or internal environment.
Perception
Is the conscious interpretation of sensations and is primarily a function of the cerebral cortex. If sensory information doesn’t reach the cerebral cortex, we have no perception of it.
Sensory modality
Each unique type of sensation – such as touch, pain, vision, or hearing. A given sensory neuron carries information for only one sensory modality.
What two classes can sensory modality be grouped into?
- General senses
- Special senses
General senses
Refer to both somatic senses and visceral senses.
Somatic senses
Include tactile sensations (touch, pressure, vibration, itch, and tickle), thermal sensations (warm and cold), pain sensations, and proprioceptive sensations. Proprioceptive sensations allow perception of both the static (nonmoving) positions of limbs and body parts (joint and muscle position sense) and movements of the limbs and head.
Visceral senses
Provide information about conditions within internal organs (Eg. Pressure, stretch, chemicals, nausea, hunger, and temperature).
Special senses
Include the sensory modalities of smell, taste, vision, hearing, and equilibrium or balance.
Sensory receptor
What the process of sensation begins at. Can either be a specialized cell or the dendrites of a sensory neuron. Responds to a particular kind of stimulus.
Stimulus
A change in the environment that can activate certain sensory receptors.
What four events take place for a sensation to arise?
- Stimulation of the sensory receptor
- Transduction of the stimulus (sensory receptor converting the energy in the stimulus into a graded potential)
- Generation of nerve impulses
- Integration of sensory input
What are the three classifications for a sensory receptors microscopic structure?
- Free nerve endings (nonencapsulated)
- Encapsulated nerve endings
- Seperate cells
Free nerve endings (nonencapsulated)
Bare dendrites associated with pain, thermal, tickle, itch, 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 retina of eye (photoreceptors), inner ear (hair cells), and taste buds of tongue (gustatory receptor cells).
Receptor potential
A graded potential generated by a sensory receptor.
What are the three classifications for a sensory receptors location and activating stimuli?
- Exteroceptors
- Interoceptors
- Proprioceptors
Exteroceptors
Located at or near body surface; sensitive to stimuli originating outside body; provide information about external environment; convey 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 usually are not consciously perceived but occasionally may be felt as pain or pressure.
Proprioceptors
Located in muscles, tendons, joints, and inner ear; provide information about body position, muscle length and tension, position and motion of joints, and equilibrium (balance).
What are the six classifications for a sensory receptors type of stimulus detected?
- Mechanoreceptors
- Thermoreceptors
- Nociceptors
- Photoreceptors
- Chemoreceptors
- Osmoreceptors
Mechanoreceptors
Detect mechanical stimuli; provide sensations of touch, pressure, vibration, proprioception, and hearing and equilibrium; also monitor stretching of blood vessels and internal organs.
Thermoreceptors
Detect changes in temperature.
Nociceptors
Respond to painful stimuli resulting from physical or chemical damage to tissue.
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.
Adaptation
A characteristic of most sensory receptors in which the receptor potential decreases in amplitude during a maintained, constant stimulus. This causes the frequency of nerve impulses in the sensory neuron to decrease. Because of adaptation, the perception of a sensation may fade or disappear even though the stimulus persists.
Rapidly adapting receptors
Adapt very quickly. They are specialized for signaling changes in a stimulus. Receptors associated with vibration, touch, and smell are rapidly adapting.
Slowly adapting receptors
Adapt slowly and continue to trigger nerve impulses as long as the stimulus persists. Slowly adapting receptors monitor stimuli associated with pain, body position, and chemical composition of the blood.
Somatic sensations
Arise from stimulation of sensory receptors embedded in the skin or subcutaneous layer; in mucous membranes of the mouth, vagina, and anus; and in skeletal muscles, tendons, and joints. The sensory receptors for somatic sensations are distributed unevenly – the areas with the highest density of somatic sensory receptors are the tip of the tongue, the lips, and the fingertips.
Cutaneous sensations
Somatic sensations that arise from stimulating the skin surface.
What are the four modalities of somatic sensation?
- Tactile sensations
- Thermal sensations
- Pain sensations
- Proprioceptive sensations
Tactile sensations
Include touch, pressure, vibration, itch, and tickle. Although we perceive differences among these sensations, they arise by activation of some of the same types of receptors.
Touch
A sensation that results from stimulation of tactile receptors in the skin or subcutaneous layer. The receptors that contribute to sensations of touch are corpuscles of touch, hair root plexuses, type I cutaneous mechanoreceptors, and type II cutaneous mechanoreceptors.
What are the two rapidly adapting touch receptors?
- Corpuscles of touch
- Hair root plexus
Corpuscles of touch (Meissner corpuscle)
Composed of a capsule that surrounds a mass of dendrites in dermal papillae of hairless skin. Senses onset of touch and low-frequency vibrations. Adapts rapidly.
Hair root plexus
Composed of free nerve endings that wrap around hair follicles in skin. Senses movements on skin surface that disturb hairs. Adapts rapidly.
What are the two slowly adapting touch receptors?
- Type I cutaneous mechanoreceptors (tactile discs)
- Type II cutaneous mechanoreceptors (Ruffini corpuscles)
Type I cutaneous mechanoreceptors (tactile discs)
Composed of saucer-shaped free nerve endings that make contact with tactile epithelial cells in the epidermis. Senses continuous touch and pressure. Adapts slowly.
Type II cutaneous mechanoreceptors (Ruffini corpuscles)
Composed of an elongated capsule that surrounds dendrites deep in the dermis and in ligaments and tendons. Senses skin stretching and pressure. Adapts slowly.
Pressure
A sustained sensation that is felt over a larger area than touch and occurs with deeper deformation of the skin and subcutaneous layer. The receptors that contribute to sensations of pressure are type I and type II cutaneous mechanoreceptors.
Vibration
A sensation that results from rapidly repetitive sensory signals from tactile receptors. The receptors that contribute to sensations of vibration are lamellated corpuscles and corpuscles of touch.
Lamellated corpuscles
Composed of an oval, layered capsule that surrounds dendrites; present in dermis and subcutaneous layer, submucosal tissues, joints, periosteum, and some viscera. Senses high frequency vibrations. Adapts rapidly.
Itch and tickle receptors
Composed of free nerve endings in skin and mucous membranes. Senses itching and tickling. Adapts slowly and rapidly.
Thermoreceptors
Free nerve endings that have receptive fields about 1mm in diameter on the skin surface.
Warm and cold receptors
Composed of free nerve endings in skin and mucous membranes of mouth, vagina, and anus. Senses warmth and cold. Initially adapts rapidly then slowly.
Nociceptors
Composed of free nerve endings in every body tissue except brain. Senses pain. Adapts slowly.
Fast pain
Occurs very rapidly, usually within 0.1 second after a stimulus is applied, because the nerve impulses propagate along medium-diameter, myelinated A fibers. This type of pain is also known as acute, sharp, or pricking pain. Fast pain is not felt in deeper tissues of the body (Eg. The pain felt from a needle puncture or knife cut).
Slow pain
Begins a second or more after a stimulus is applied. It then gradually increases in intensity over a period of several seconds or minutes. Impulses for slow pain conduct along small-diameter, unmyelinated C fibers. This type of pain, which may be excruciating, is also referred to as chronic, burning, aching, or throbbing pain. Slow pain can occur both in the skin and in deeper tissues or internal organs (Eg. The pain associated with a toothache).
Superficial somatic pain
Pain that arises from stimulation of receptors in the skin.
Deep somatic pain
Pain that arises from stimulation of receptors in skeletal muscles, joints, tendons, and fascia.
Visceral pain
Pain that arises from stimulation of nociceptors in visceral organs.
Referred pain
When pain is felt in or just deep to the skin the overlies the stimulated organ, or in a surface area far from the stimulated organ. In general, the visceral organ involved and the area to which the pain is referred are served by the same segment of the spinal cord.
Analgesia
Pain relief.
Proprioceptive sensations
AKA proprioception; allow us to recognize that parts of our body belong to us (self). They also allow us to know where our head and limbs are located and how they are moving even if we are not looking at them.
Kinesthesia
The perception of body movements.
Proprioceptors
The receptors that proprioceptive sensations arise from. Are found embedded in muscles (especially postural muscles) and tendons. Inform us of the degree to which muscles are contracted, the amount of tension on tendons, and the positions of joints.
Weight discrimination
The ability to assess the weight of an object.
Muscle spindles
Composed of sensory nerve endings that wrap around the central area of encapsulated intrafusal muscle fibers within most skeletal muscles. Senses muscle length. Adapts slowly.
Muscle tone
The small degree of contraction that is present while the muscle is at rest.
Intrafusal muscle fibers
Within muscle spindles.
Gamma motor neurons
Innervate ends of the intrafusal muscle fibers and stimulate them to contract. Has cell bodies in the anterior gray horn of the spinal cord (or in the brainstem for muscles in the head).
Extrafusal muscle fibers
Surrounding muscle spindles.
Alpha motor neurons
Innervate extrafusal muscle fibers and stimulate them to contract. Has cell bodies in the anterior gray horn of the spinal cord (or in the brainstem for muscles in the head).
Tendon organs
Composed of a capsule that encloses collagen fibers and sensory nerve endings at the junction of a tendon and a muscle. Senses muscle tension. Adapts slowly.
Tendon fascicles
Bundles of collagen fibers that are enclosed by a thin capsile of connective tissue. Make up tendon organs.
Joint kinesthetic receptors
Composed of lamellated corpuscles, type II cutaneous mechanoreceptors, tendon organs, and free nerve endings. Senses joint position and movement. Adapts rapidly.
Somatic sensory (somatosensory) pathways
Relay information from somatic sensory receptors to the primary somatosensory area (postcentral gyrus) in the parietal lobe of the cerebral cortex and to the cerebellum.
What three types of neurons make up the somatic sensory (somatosensory) pathways?
- First-order (primary) neurons
- Second-order (secondary) neurons
- Third-order (tertiary) neurons
First-order (primary) neurons
Are sensory neurons that conduct impulses from somatic sensory receptors into the brainstem or spinal cord.
Second-order (secondary) neurons
Conduct impulses from the brainstem or spinal cord to the thalamus. Axons of second-order neurons decussate (cross over to the opposite side) as they course through the brainstem or spinal cord before ascending to the thalamus.
Third-order (tertiary) neurons
Conduct impulses from the thalamus to the primary somatosensory area on the same side. As the impulses reach the primary somatosensory area, perception of the sensation occurs.
Relay stations
Regions within the CNS where neurons synapse with other neurons that are a part of a particular sensory or motor pathway. At these relay stations, neural signals are being relayed from one region of the CNS to another (Eg. The thalamus is a major relay station).
Posterior column-medial lemniscus pathway
Conveys nerve impulses for touch, pressure, vibration, and conscious proprioception from the limbs, trunk, neck, and posterior head to the cerebral cortex.
Posterior (dorsal) columns
Formed by the axons of first-order neurons in the spinal cord.
What are the two major tracts that form the posterior (dorsal) columns?
- Gracile fasciculus
- Cuneate fasciculus
Gracile fasciculus
Conveys nerve impulses for touch, pressure, vibration, and conscious proprioception from lower limbs and lower trunk.
Cuneate fasciculus
Coveys nerve impulses for touch, pressure, vibration, and conscious proprioception from upper limbs, upper trunk, neck, and posterior head.
Medial lemniscus
A thin ribbonlike projection tract that extends from the medulla to the ventral posterior nucleus of the thalamus.
Anterolateral (spinothalamic) pathway
Conveys nerve impulses for pain, cold, warmth, itch, and tickle from the limbs, trunk, neck, and posterior head to the cerebral cortex.
Trigeminothalamic pathway
Conveys nerve impulses for most somatic sensations (tactile, thermal, and pain) from the face, nasal cavity, oral cavity, and teeth to the cerebral cortex.
The ______ and the ______ relate body parts to cortical areas.
Somatic sensory map; somatic motor map.
Primary somatosensory area
Occupies the postcentral gyri of the parietal lobes of the cerebral cortex. Each region in this area receives sensory input from a different part of the body, which causes precise localization of somatic sensations.
Sensory homunculus
Distorted somatic sensory map of the body.
Anterior and posterior spinocerebellar pathways
Convey nerve impulses from proprioceptors in trunk and lower limb of one side of body to same side of cerebellum. Proprioceptive input informs cerebellum of actual movements, allowing it to coordinate, smooth, and refine skilled movements and maintain posture and balance.
What is the difference between anterior and posterior spinocerebellar pathways?
The anterior spinocerebellar pathway decussates twice, whereas the posterior spinocerebellar pathway only decassates once.
What orchestrates all voluntary movements?
Neural circuits in the brain and spinal cord
Lower motor neurons (LMNs)
Neurons that have their cell bodies in the lower parts of the CNS (brainstem and spinal cord). Provide output from the CNS to skeletal muscle fibers, stimulating contraction of skeletal muscles.
What four neurons provide input to lower motor neurons (LMNs)?
- Local circuit neurons
- Upper motor neurons (UMNs)
- Basal nuclei neurons
- Cerebellar neurons
Local circuit neurons
Help coordinate rhythmic activity in specific muscle groups, such as alternating flexion and extension of the lower limbs during walking.
Upper motor neurons
Upper motor neurons from the cerebral cortex are essential for the planning and execution of voluntary movements of the body. Other upper motor neurons originate in motor centers of the brainstem and help regulate posture, balance, muscle tone, and reflexive movements of the head and trunk.
Basal nuclei neurons
Help initiate and terminate movements, suppress unwanted movements, and establish a normal level of muscle tone.
Cerebellar neurons
Coordinates body movements and helps maintain normal posture and balance.
What two components of the cerebral cortex contribute to body movement?
- Premotor area
- Primary motor area
Premotor area
Where a motor plan is developed. This plan identifies which muscles should contract, how much they need to contract, and in what order. Also stores information about learned motor activities.
Primary motor area
Is the major control region for the execution of voluntary movements. Electrical stimulation of any point in the primary motor area causes contraction of specific muscles on the opposite side of the body. The primary motor area controls muscles by forming descending pathways that extend to the spinal cord and brainstem.
Motor homunculus
Distorted muscle map of the body.
What four components of the brainstem contribute to body movement?
- Vestibular nuclei
- Reticular formation
- Superior colliculus
- Red nucleus
How does the basal nuclei contribute to body movement?
- Initiation of movements
- Suppression of unwanted movements
- Regulation of muscle tone
- Regulation of nonmotor processes
How does the cerebellum contribute to body movement?
- Monitoring intentions for movement
- Monitoring actual movement
- Comparing command signals with sensory information
- Sending out corrective feedback
Direct motor pathways
AKA pyramidal pathways; provide input to lower motor neurons via axons that extend directly from the cerebral cortex. Govern generation of action potentials in the lower motor neurons.
What are the three direct motor pathways?
- Lateral corticospinal pathway
- Anterior corticospinal pathway
- Corticobulbar pathway
Pyramidal cells
Are upper motor neurons that have pyramid-shaped cell bodies. Are the main output cells of the cerebral cortex.
Lateral corticospinal pathway
The 90% of the corticospinal pathway that does decussate. Conduct nerve impulses for the control of muscles of the limbs and trunk.
Anterior corticospinal pathway
The 10% of the corticospinal pathway that doesn’t decussate. Conduct nerve impulses for the control of muscles of the limbs and trunk.
Corticobulbar pathway
Conducts nerve impulses for the control of skeletal muscles in the head.
Indirect motor pathway
AKA extrapyramidal pathways; provide input to lower motor neurons from motor centers in the brainstem. In general, conduct action potentials to cause involuntary movements that regulate posture, balance, muscle tone, and reflexive movements of the head and trunk.
What are the five indirect motor pathways?
- Rubrospinal pathway
- Tectospinal pathway
- Vestibulospinal pathway
- Lateral reticulospinal pathway
- Medial reticulospinal pathway
Rubrospinal pathway
Conveys nerve impulses from red nucleus (which receives input from cerebral cortex and cerebellum) to contralateral skeletal muscles that govern precise, voluntary movements of distal parts of upper limbs.
Tectospinal pathway
Conveys nerve impulses from superior colliculus to contralateral skeletal muscles that reflexively move head, eyes, and trunk in response to visual or auditory stimuli.
Saccades
Small, rapid jerking movements of the eyes that occur as a person looks at different points in the visual field. The superior colliculus is an integrating center for these.
Vestibulospinal pathway
Conveys nerve impulses from vestibular nucleus (which receives input about 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.
Postural reflexes
Keep the body in an upright and balanced position. Input for postural reflexes comes from three sources: 1.) the eyes, 2.) the vestibular apparatus of the inner ear, 3.) proprioceptors in muscles and joints.
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.
Integration
The processing of sensory information by analyzing and storing it and making decisions for various responses.
Integrative functions
Include cerebral activities such as sleep and wakefulness, learning and memory, and language.
Circadian rhythm
24-hour sleep and awaken cycle. Established by the suprachiasmatic nucleus of the hypothalamus.
Reticular activating system (RAS)
Helps nervous system make the transition between sleep and wakefulness. When the RAS is active, it transmits many nerve impulses to widespread areas of the cerebral cortex, both directly and via the thalamus. This results in a generalized increase in cortical activity.
Arousal
Awakening from sleep. Also involves increased activity in the RAS. For arousal to occur, the RAS must be stimulated. Many sensory stimuli can activate the RAS.
Consciousness
A state of wakefulness.
Coma
A state of unconsciousness in which an individual has little or no response to stimuli.
Persistent vegetable state
Occurs after weeks of being in a coma. An individual in this state has normal sleep-wake cycles but does not have an awareness of their surroundings. They are unable to speak or to respond to commands. They may smile, laugh, or cry, but do not understand the meaning of these actions.
Learning
The ability to acquire new information or skills through instruction or experience.
What are the two main categories of learning?
- Associative learning
- Nonassociative learning
Associative learning
Occurs when a connection is made between two stimuli.
Nonassociative learning
Occurs when repeated exposure to a single stimulus causes a change in behavior.
What are the two types of nonassociative learning?
- Habituation
- Sensitization
Habituation
Repeated exposure to an irrelevant stimulus causes a decreased behavioral response.
Sensitization
Repeated exposure to a noxious stimulus causes an increased behavioral response.
Language
A system of vocal sounds and symbols that conveys information. Most commonly it is spoken and/or written.
Language areas
Found in the cerebral cortex; usually only present in the left cerebral hemisphere.
What are the two language areas?
- Wernicke’s area
- Broca’s area
Wernicke’s area
An association area found in the temporal lobe, that interprets the meaning of written or spoken words. It essentially translates words into thoughts. Receives input from the primary visual area (for written words) and from the primary auditory area (for spoken words).
Sleep
A state of altered consciousness or partial unconsciousness from which an individual can be aroused. Induced by adenosine.
What are the two component’s of sleep?
- Non-rapid eye movement (NREM) sleep
- Rapid eye movement (REM) sleep
What are the four stages of non-rapid eye movement (NREM) sleep?
Stage 1: is a transition stage between wakefulness and sleep that normally lasts 1-7 minutes. The person is relaxed with eyes closed and has fleeting thoughts. People awakened during this stage often say they have not been sleeping.
Stage 2: AKA light sleep; Is the first stage of true sleep. In it, a person is easy to awaken. Fragments of dreams may be experienced, and the eyes may slowly roll from side to side.
Stage 3: is a period of moderately deep sleep. Body temperature and blood pressure decrease, and it is a little more difficult to awaken the person. This stage occurs about 20 minutes after falling asleep.
Stage 4: is the deepest level of sleep. Although brain metabolism decreases significantly and body temperature drops slightly at this time, most reflexes are intact, and muscle tone is decreased only slightly. During this stage, it is very difficult to awaken a person.
Rapid eye movement (REM) sleep
AKA paradoxical sleep; when most dreaming occurs. Neuronal activity is high during this sleep.
NREM sleep centers
Induces NREM; in the hypothalamus and basal forebrain.
REM sleep center
Promotes REM; in the pons and midbrain.
Memory
The process by which information acquired through learning is stored and retrieved.
What are the two main types of memory?
- Declarative (explicit) memory
- Procedural (implicit) memory
Declarative (explicit) memory
The memory of experiences that can be verbalized (declared) such as facts, events, objects, names, and places. This type of memory requires conscious recall and is stored in the association areas of the cerebral cortex.
Procedural (implicit) memory
The memory of motor skills, procedures, and rules. This type of memory does not require conscious recall, and it is stored in the basal nuclei, cerebellum, and premotor area.
Short-term memory
The temporary ability to recall a few pieces of information for seconds to minutes.
Long-term memory
More permanent type of memory that lasts from days to years.
Memory consolidation
The process by which a short-term memory is transformed into a long-term memory. The hippocampus plays a major role in the consolidation of declarative memories.
Plasticity
The capability for change associated with learning.
Long-term potentiation (LTP)
A phenomenon that is believed to underlie some aspects of memory. Transmission at some synapses within the hippocampus is enhanced (potentiated) for hours or weeks after a brief period of high-frequency stimulation.
