Neuro - Part 3 Flashcards
Describe the organization of the sensory nervous system
- sensory input and motor input are primarily mediated by the PNS
- sensory input pathways include: sensory reception, transduction, amplification and adaption, transmission, integration, and perception.
- environment > PNS sensory input > CNS unconscious (and conscious) integration > PNS motor output > environment
The nervous system monitors somatic and visceral sense to: ___________. How?
- maintain proper functions of the body
- sensory receptors in every tissue of the body acquire sensory information at the terminal end of spinal and cranial sensory nerve fibers, and convey it to the CNS for processing
- can be detectable (pain, touch, temp, bladder) or not (blood pressure, O2, CO2 levels)
What are the kinds of sensory signals?
- somatosensory signals
- viscerosensory signals
What are the particularities of somatosensory and viscerosensory signals?
- somatosensory
- originate from cutaneous area, muscle, joints
- respond to mechanical, chemical, or thermal stimuli
- vision and hearing are special somatic
- viscerosensory
- originate from internal structures
- some are consciously detectable (ex: stretching of stomach/bladder)
- taste and gustation are special visceral
What is the “labeled line” principle?
- the specificity of nerve fibers for transmitting only one modality of sensation
- when a specifc sensory fiber is stimulated, perception is related to the fiber type not the stimulus type (ex: pain receptors only receive pain)
Sensory fibers make connections with local circuitry for _____________ or travel ______________ to synapse in specific regions of the brain (brainstem, cerebellum, thalamus, cerebral cortex)
- reflex functions, cranially
Nerve fibers are classified ether by _________classification or _________ classification
- general (Erlanger-Gasser)
- numerical (Lloyd + Hunt)
What are the features of general and numerical classification?
General classification
- applies to both sensory + motor fibers
- type A: typically large/medium-sized myelinated fibers of spinal nerves (alpha, beta, gamma, g)
- type B: small, myelinated, preganglionic autonomic fibers
- type C: small unmyelinated nerve fibers that conduct impulses at low velocities, constitute more than 1/2 of the sensory fibers in most peripheral nerves and postganglionic autonomic fibers
Numerical classification
- only applies to sensory fibers
- I (a+b), II, III, IV
What are the kinds of receptors?
Structural classification:
- simple receptors
- complex receptors
- special senses receptors
Functional classification:
- mechanoreceptors
- thermoreceptors
- nocireceptors
- photoreceptors
- chemoreceptors
What is a sensory receptor?
- a nerve ending, cell or group of cells, or a sense organ that when stimulated produces an afferent or sensory impulse
What are the features of simple, complex, and special sense receptors?
- simple receptors
- no special modification - free nerve endings
- not myelinated
- most common
- complex receptors
- ensheathed by CT capsule
- encapsulated portions of axon are not myelinated
- special senses receptors
- specialized receptor cells
What are features of mechanoreceptors?
- receptors for:
- skin tactile senses (dermis/epidermis)
- ex: free nerve ending, merkel’s discs, ruffini’s endings, meissners corpuscles, krauses corpuscles, hair end organs
- deep tissue sensibilities
- ex: ruffini’s endings, pacinian corpuscles, muscle spindles, golgi tendon receptors
- hearing
- sound receptors of cochlea
- equilibrium/balance
- vestibular receptors
- arterial receptors
- baroreceptors of carotid sinuses/aorta
- skin tactile senses (dermis/epidermis)
What are features of thermoreceptors?
- receptors for feeling temperature
- warm receptors
- cold receptors
- all are free nerve endings
What are features of nociceptors?
- receptors for pain
- free nerve endings
What are features of photoreceptors?
- receptors for vision
- rods + cones
What are features of chemoreceptors?
- receptors for:
- taste: receptors of taste buds
- smell: receptors of olfactory epithelium
- arteial O2: receptors of aortic/carotid sinus
- osmolality: neurons in/near supraortic nuclei
- blood O2: receptors in/on surface of medulla + in aortic/carotid bodies
- blood glucose, AA, FA: receptors in hypothalamus
What are muscle spindles?
- mechanoreceptors
- encapsulated group of ~3-12small,sender,specialized skeletal muscle fibers
What are some features of muscle fibers?
- contractile elements are restricted to the ends (none in the middle)
- the middle is innervated by sensory neurons and carry APs from the spindle to the CNS
- there are intrafusal and extrafusal fibers
- are stretch receptors who function to correct changes in muscle length
What are the differences between intrafusal and extrafusal muscle fibers
- intrafusal
- too small to generate significant force
- attached to a extracellular matrix of extrafusal fibers
- innervated by gamma moor neurons (give rise to type A gamma fibers)
- extrafusal
- majority of skeletal muscle fibers
- used to generate force
- innervated by alpha motor neurons (give rise to type A alpha fibers)
What is the function of muscle spindles?
- sense STRETCH (stretch receptors)
- function to correct for hangers in muscle length
- stretching the middle segment of the INTRAFUSAL fiber generates AP along the spindle sensory neurons
- stretch sensitive ion channels open leading to membrane depolarization and AP generation
- the muscle contracts
What is the golgi tendon organ?
- encapsulated sensory receptor through which muscle tendon fibers pass
- 10-15 muscle fibers usually connected to each
- stimulated when the muscle fiber bundle is tensed by contraction of the muscle
What is the function of the golgi tendon organ?
- provide the nervous system with information on the degree of tension in each segment of muscle via signals conducted through large rapidly conducting sensory nerve fibers
- inhibit alpha motor neuron activity
- cause muscle RELAXATION
- proves excess tension on the muscle
Muscle spindle participates in sensory and motor function. Co-activation of ___________ and ___________ allow the brain to tes whether the amount of _____________ intended by the brain is what actually occurred.
- alpha and gamma neurons
- contraction
What is a receptor potential?
- also known as generator potential
- whatever the type of stimulus, its immediate effect is of change in the membrane electrical potential of the receptor
What are the 4 ways a receptor potential can be stimulated?
- mechanical deformation
- application of a chemical to the membrane
- change of the temperature of the membrane
- the effects of electromagnetic radiation (like light on a retinal visual receptor)
What is amplification of receptors?
- the relationship between receptor potential and action potential in that:
- the intensity of the stimulus can be changed by the frequency of action potentials and the number receptors activated
What is adaption of receptors?
- the ability of a sensory receptor to adapt it her partially or completely to any constant stimulus after a period of time
- when a continuous sensory stimulus is applied, the receptor responds at a high impulse rate initially, which then gets progressively slower until the rate of APs is very few/none
What is sensory adaptation?
- ability to diminish the extent of depolarization despite sustained stimulus strength
What are the kinds of adaptive sensory receptors?
- slow adapting “TONIC” receptors
- continue to transmit impulses to the brain as long as the stimulus is presen, or at least forming/hours
- ex: baroreceptors, chemoreceptors
- ** pain receptors usually NEVER adapt
- fast adapting “PHASIC” receptors
- stimulated only when stimulus strength CHANGES
- ex: pacinian corpuscle: skin deep pressure
T/F: Pacinian corpuscles are a tonic receptor, meaning they are fast adapting
- False; phasic receptor
What is a dermatome?
- areas of the skin innervated by cutaneous branches from a single spinal nerve
What does stimulus perception describe?
- ability of animals to detect different modalities of stimulus and know the location of a stimulus applied to the body
- each segment of the spinal cord innervates a specific receptive field of the body (dermatome)
- trigeminal nerve (CN V) fibers have specific receptive fields on the face
What is acuity?
- precision of stimulus location, receptive fields of specific afferent neurons code for the stimulus location
What is acuity dependent on?
- size and # of receptive fields
- smaller field = greater acuity
- ex: lips/fingers have greater acuity than the back/shoulders due to 2-point discrimination
- smaller field = greater acuity
- lateral inhibition
What is 2-point discrimination?
- the ability to perceive two fine points as two separate stimuli and not one
What is lateral inhibition?
- the inhibition of transmission of signals of neurons with neighboring fields, in response to application of a strong stimulus to the receptive field of one neuron
- increases acuity by increasing contrast of signals in the nervous system
What are somatic sensations?
- sensations detected by peripheral receptors including touch, pain, temperature, and position of the body
What are somesthetic tracts? A nerve tract? Ascending somatosensory pathways?
- ascending spinal tracts that mediate signals from somatosensory receptors and reach the brainstem; thalamus + cerebellum
- a nerve tract is a bundle of nerve fibers (axons) connecting nuclei of the CNS
- specific modality neurons that carry signals to specific areas o the thalamus which then projects to specific areas of the somatosensory cerebral cortex
What is nociception?
- “pain”
-the conscious perception of noxious stimulus, accompanied by unpleasant emotional response
What are nociceptors? Some features?
- free nerve endings that are widespread in the superficial layers of the skin and certain internal tissues
- ex: periosteum, arterial walls, joint surfaces, specific areas of the skull
- do NOT adapt or adapt very little to stimulus
T/F: a noxious stimulus always results in the experience of pain
- false; a noxious stimulus may simulate a variety of somatic and autonomic responses and reflexes
- it MAY also be transmitted to the brain and result in the experience of pain
Pain is transmitted via 2 type of fibers:
- A delta fibers: “fast pain”
- C fibers: “slow pain”
- both fibers enter via the dorsal root and synapse in the dorsal horn
- from there,connections are made within or between segments for reflex activity such as the withdrawal reflex
- pain will also be transmitted cranially in a variety of pathways found in all funiculi
What are some features of A delta fibers?
- nociceptors
- transmit fast pain
- felt within 0.1 seconds after pain stimulus
- “superficial pain”
- mostly originated in skin
- sharp, well-localized pain
- warn brain of potential tissue damage
What are some features of C fibers?
- nociceptors
- transmit slow pain
- begins after 1+ seconds, and increases slowly over seconds/minutes
- “deep pain”
- originated from skin or deeper structures
- associated w tissue destruction
- lead to prolonged unbearable suffering
- cause individuals to withdraw and rest aiming to promote healing
For a spinal cord lesion to cause loss of nociception there must be:
The presence of absence of deep pain perception is important to:
- extensive destruction across the width of the cord to destroy all tracts
- assess the prognosis for recovery from severe spinal cord injuries
- withdrawal of limb indicates only an intact reflex
- behavioral response indicates conscious perception of pain!
What are the 3 types of stimuli that can excite pain receptors?
- mechanical
- thermal
- chemical
- mechanical and thermal are both slow + fast pain, chemical is only slow pain
T/F: pain can be exogenously modulated by the NS
- true; the body can inhibit pain conduction through central and peripheral antinociceptive mechanisms
- stimulation of many CNS areas are mediated by release or alterations of neurotransmitter concentration
- pain transmission can be blocked locally at the spinal cord
Enkephalin and endorphin act in the CNS to _________ presynaptic neurons transmitting pain sensation
- inhibit
- neurotransmitters bind to opioid receptors + terminate pain signals by inhibiting release to substance P from pre-synaptic neurons
Pinprick axons form collaterals that project and excite short ___________________. What does this do?
- inhibitory enkephalinergic interneurons
- inhibits neurons that project pain
What is proprioception?
- knowledge of one’s position: can be conscious or subconscious
- dependent on knowing the degrees of angulation of all joints in all planes and their rates of change
What receptors are important for proprioception?
- skin tactile receptors and deep receptors near joints
- muscle spindles, golgi tendon organ
- pacinian corpuscles (deep pressure)
- ruffini’s ending (continuous pressure)
-hair cells (receptors) in the vestibular apparatus of the inner ear supply information about head position and movement
How does proprioceptive information travel?
- from peripheral receptors via spinal nerves, dorsal lot, and spina cord, to brain
- information terminates in the somatosensory cortex of the CONTRALATERAL CEREBRUM is used in conscious proprioception
- information terminating in the IPSILATERAl CEREBELLUM is used in subconscious proprioception
What are the differences between conscious and subconscious proprioception?
- conscious proprioception
- conscious awareness of body position + movement of bod walls
- enables cerebral cortex to plan and refine voluntary, learned movements
- unconscious proprioception
- based around stretch and tension of muscles, tenons, and ligaments; at rest and during movement, and spatial orientation of the body
- cerebellum needs this info to coordinate posture and locomotion
Why is the vestibular system important in proprioception?
It provides proprioceptive information (conscious/subconscious) about head position and movement, fundamental for setting the balance and posture of the animal
T/F: you can always make the distinction clinically between conscious and subconscious proprioceptive deficits.
- False; not always possible
- conscious proprioceptive deficits: typified by animal bearing weight on an abnormal part of the foot, ex: dorsum of paw
- subconscious proprioceptive deficits: typified by abnormal position of the limbs with respect to center of gravity, at rest and locomotion, ex: hopping test
What are visceral sensations? What receptors are responsible?
- viscerosensory signals that are essential for respiration, heart rate , blood pressure, and micturition
- sensory receptor of the viscera are composed primarily of free nerve endings
** primarily nociceptors and physiological receptors
What are some features of nociceptors in the viscera?
- detect changes in visceral structures caused by abnormal physical conditions or pathological conditions
- ex: gi bloating, cramping, peritonitis
- visceral organs are not sensitive to cutting, heat,or cold
- would need A fibers
- viscera responds to stretching, distinction, spasm, inflammation, and ischemia
- diffuse type stimulus = C fibers
- visceral pain is poorly localized
- few general afferent fibers - infrequently recognized by conscious perception
What are some features of physiological receptors in the viscera?
- receptors that respond to innocuous (normal) stimuli
- 2 Types: mechanoreceptors + chemoreceptors
- changes in blood pressure
- changes in pCO2 or pO2
- coughing reflex: receptors sensitive to inhaled particles in the respiratory system
- sense of fullness: stretch or tension in the smooth muscle layer (ex: stomach, urinary bladder)
Viscerosensory afferent fibers are carried by:
- sympathetic + parasympathetic nerves
- physiologic receptors send information primarily through viscerosensory fibers of parasympathetic nerves
- nociceptors send information through viscerosensory fibers of sympathetic nerves
** although viscerosensory fibers are a structural component of both sympathetic/parasympathetic nerves, they are not considered part of the ANS
What is the functions of taste and smell?
- work together in several processes (ex: choosing food, physiological responses involved in digestion, recognition)
- both senses are strongly tied to primitive emotional and behavioral fxns of the nervous system
What does the olfactory system consist of?
- olfactory bulb
- olfactory tracts
- lateral olfactory gyrus
- piriform lobe
What is the olfactory system essential for?
- localization of food
- reflex stimulated secretion of digestive enzymes
- detection of danger
Olfactory cells are part of the specialized epithelium found on the ethmo-turbinate bones of the nasal cavity. They are receptor cells for smell sensation with what features?
- bipolar neurons derived originally from the CNS
- located in the olfactory epithelium interspersed among supporting cells
- have cilia projecting into the mucus that coats the inter surface of the nasal cavity that react to odors in the air and stimulate olfactory cels
- spaced among the olfactory cels are many olfactory glands
- secrete mucus
The olfactory cilia responds to olfactory chemical stimuli. How?
What is the central pathway for olfaction?
- olfactory nerve fibers terminate + synapse in the olfactory bulb to form the olfactory tract (CN I)
- specific cells are present in the olfactory bulb
- tufted cells
- mitral cells
- dendrites of the cells synapse w/ terminal ends of olfactory cells forming the glomeruli of the olfactory bulb
- neurotransmitters excite these cells
- specific cells are present in the olfactory bulb
What is the relationship between taste/smell and the limbic system?
- the olfactory tract reaches the preform lobe as well as nonolfactory portions of the brain that are part of the limbic system
- amygdala, entorhinal cortex, hippocampal formation, septal nuclei
- these areas also send olfactory signals to the hippocampus and frontal cortex
- amygdala, entorhinal cortex, hippocampal formation, septal nuclei
- the limbic system is responsible for forming olfactory memories, so that olfaction can evoke emotional and autonomic responses
- there are many connections between the olfactory and gustatory systems and the regions responsible for emotion an memory
