Chapter 13
Describe how spinal nerves arise from the spinal cord.
31 pairs of spinal nerves, each containing thousands of nerve fibers, arise from the spinal cord and supply all parts of the body except the head and some areas of the neck. All are mixed nerves. 8 pairs of cervical nerves 12 pairs of thoracic 5 pairs of lumbar 5 pairs of sacral 1 pair of tiny coccygeal Each spinal nerve connects to the spinal cord by a dorsal root and a ventral root. Each root forms from a series of rootlets that attach along the length of the corresponding spinal cord segment. Ventral roots: contain motor (efferent) fibers that arise from ventral horn motor neurons and extend to and innervate the skeletal muscles. Dorsal roots: contain sensory
Describe the general structure of a nerve
A cordlike organ that is part of the peripheral nervous system; classified as cranial or spinal depending on whether they arise from the brain or spinal cord; vary in size but every nerve consists of parallel bundles of peripheral axons (Some myelinated and some not) enclosed by wrappings of connective tissues PG 492-493
Briefly explain how regeneration of a PNS neuron takes place. Why does the same thing not happen in the CNS?
Damage to nervous tissue is serious because mature neurons do not divide. If the damage is severe or close to the cell body, the entire neuron may die, and other neurons that are normally stimulated by its axon may die as well. However if the cell body remains intact, axons of peripheral nerves can regenerate but axons in the CNS cannot.
Explain the classification of sensory receptors by stimulus type.
Mechanoreceptors: respond to mechanical force such as touch, pressure (including blood pressure), vibration and stretch. Thermoreceptors: respond to temperature changes Photoreceptors: such as those of the retina of the eye, respond to light Chemoreceptors: respond to chemicals in solution (molecules smelled or tasted, or changes in blood or interstitial fluid chemistry) Nociceptors: respond to potentially damaging stimuli that result in pain. For example. searing heat, extreme cold, excessive pressure, and inflammatory chemicals are all interpreted as painful. These signals stimulate subtypes of thermoreceptors mechanoreceptors, and chemoreceptors.
Explain visceral pain. Explain referred pain.
Results from noxious stimulation of receptors in the organs of the thorax and abdominal cavity. Like deep somatic pain, or burning. Important stimuli for visceral pain are extreme stretching of tissue, ischemia (low blood flow), irritating chemicals and muscle spasms. The fact that visceral pain afferents travel along the same pathways as somatic pain fibers helps explain the phenomenon of referred pain, in which pain stimuli arising in one part of the body are perceived as coming from another part.
What do the thoracic spinal nerves innervate?
Thoracic spinal nerves innervate the anterior and lateral thorax and abdominal muscles. They form the intercostal (and subcostal) nerves.
What is transduction? Explain the difference between generator potentials and receptor potentials.
Transduction: The stimulus energy must be converted into the energy of a graded potential. This graded potential may be depolarizing or hyperpolarizing, similar to the EPSPs or IPSPs generated at postsynaptic membranes in response to neurotransmitter binding Generator potential: receptors can produce one of two types of graded potentials. When the receptor region is part of a sensory neuron as with free dendrites or the encapsulated receptors of most general sense receptors, the graded potential; because it generates action potential in a sensory neuron Receptor potential: When the receptor is a separate cell, the graded potential is called receptor potential, because it occurs in a separate receptor cell. The receptor potential changes the amount of neurotransmitter released by the receptor cell onto the sensory neuron. The neurotransmitters then generate graded potentials in the sensory neuron
What is a plexus?
all ventral rami branch and join one another lateral to the vertebral column forming complicated interlacing nerve networks
What is a dermatome?
is an area of skin innervated by the cutaneous branches of a spinal nerve
Explain the classification of sensory receptors by location.
Exteroceptors: are sensitive to stimuli arising outside the body, so most exteroceptors are near or at the body surface. They include touch, pressure, pain and temperature receptors in the skin and most receptors of the special sense Interoceptors: also called visceroceptors, respond to stimuli within the body such as from the internal viscera and blood vessels. Interoceptors monitor a variety of stimuli, including chemical changes, tissue stretch, and temperature. Sometimes their activity causes us to feel pain, discomfort, hunger or thirst. However, we are usually unaware of their workings. Proprioceptors: like interoceptors, respond to internal stimuli. However, their location is much more restricted; occur in skeletal muscles, tendons, joints, ligaments and in connective tissue coverings of muscles and bones; constantly advise the brain of our body movements by monitoring how much the organs containing these receptors are stretched.
What is nociception? What is its function?
Nociception: Pain stimuli. FX. is to provide information that damage is occurring to the body and to stimulate the subtypes to take steps to repair and prevent damage. Heat and cold outside the range of thermoreceptors activates NOCICEPTORS. This respond to pinch and chemicals released from damaged tissue. Another key player in detecting painful stimuli is VANILLOID RECEPTOR. An ion channel that is opened by heat, low pH, and various chemicals including capsaicin, the substance found in chili peppers.
List and explain the components necessary for perception.
processing of sensory information can occur at any time in the journey from transduction at the receptor to the cerebral cortex: 1. receptor level- sensory receptors 2. circuit- in ascending pathway 3. perceptual level- cortex For sensation to occur a stimulus must excite a receptor and action potential must reach CNS. 1.stimulus- environmental change to which the receptor will respond. in addition this stimulus must be applied within the receptor's receptive field(area monitored by receptor) 2. sensory receptor: sensitive to stimulus. if a receptor is a neuron, it responds to a stimulus by producing an action potential AP= Generator potential. Some receptors do not generate AP, their response to a stimulus is called receptor potential.( special sense) continually release neurotransmitter. The receptor changes how much neurotransmitter they are releasing onto a sensory neuron. -Sensory neuron then generates an action potential. -sensory area of cortex
Name, locate and give the function of the 12 pairs of cranial nerves.
I. Olfactory: These are tiny sensory nerves (filaments) of smell, which run from the nasal mucosa to synapse with the olfactory bulbs. Note that the olfactory bulbs and tracts, shown in fig. 13.6a are brain structures and not part of cranial nerve I. (see table 13.2 for the olfactory nerve filaments) II. Optic: Because this sensory nerve of vision develops as an outgrowth of the brain, it is really a brain tract. III. Oculomotor: The name means "eye mover" This nerve supplies four of the six extrinsic muscles that move the eyeball in the orbit. IV. Trochlear: The term means "pulley" and it innervates an extrinsic eye muscle that loops through a pulley-shaped ligament in the orbit V.Trigeminal: Pg 495-496, 502-503
Briefly describe the components of the CNS that are responsible for producing and controlling body movements. How do they accomplish this?
In order for your CNS to control movements of your body, there is a chain of command. The primary motor cortex says "do this." A plan of how to accomplish the desired activity is put together by the cerebellum and sent back to the cortex. The cortex then issues the commands to perform the movement. These commands come down the motor pathways and activate two systems: central pattern generators (circuits that control specific, often repeated movements such as stepping, these are controlled by the indirect pathways) and direct pathways that produce discrete (i.e., singular) movements. The body starts performing the movement and proprioceptive information is fed back up to the cerebellum and basal nuclei. These provide feedback to make the movement conform to that asked for by the cortex and to make it more efficient.
Explain adaptation of a sensory receptor. Distinguish between phasic and tonic receptors.
Information about a stimulus-its strength, duration and patter is encoded in the frequency of nerve impulses: the greater the frequency, the stronger the stimulus. Many but not all sensory receptors exhibit adaptation, a change in sensitivity and nerve impulse generation in the presence of a constant stimulus. For example, when you step into bright sunlight from a darkened room, your eyes are initially dazzled, but your photoreceptors rapidly adapt, allowing you to see both bright areas and dark areas in the scene Phasic receptors: are fast adapting, often giving bursts of impulses at the beginning and the end of the stimulus(the time when things are changing) report changes in the internal or external environment. Examples are lamellar and tactile corpuscles Tonic receptors: provide a sustained response with little or no adaptation. Nociceptors and most proprioceptors are tonic receptors because of the protective importance of their information, continue to signal pain until the stimulus stops and the area is healed
Distinguish between encapsulated and unencapsulated sensory receptors.
Nonencapsulated (Free) Nerve Endings: present nearly everywhere in the body; particularly abundant in epithelia and connective tissues. Most of these sensory fibers are nonmyelinated, small-diameter group C fibers, and their distal endings (the sensory terminals) usually have small knoblike swellings. FX: for pain, tempt, and mechanoreception. Another key player in detecting painful stimuli is VANILLOID RECEPTOR. An ion channel that is opened by heat, low pH, and various chemicals including capsaicin, the substance found in chili peppers. Another sensation mediated by free nerve endings are itch. An ITCH receptor, located in the dermis, escaped detection for years because of its thin diameter. A number of chemicals-notably histamine-present at inflamed sites activate nerve endings. Other nonencasulated nerve endings: Tactile (Merkel) discs: which lie in the deepest layer of the epidermis, function as light touch receptors. Certain free nerve endings associate with enlarged, disc-shaped epidermal cells Hair follicle receptors: free nerve endings that wrap basketlike around hair follicles, are light touch receptors that detect movement of hairs shaft. The tickle of a mosquito landing on your skin is mediated by hair follicle receptors. Encapsulated Nerve Endings: consist of one or more fiber terminals of sensory neurons enclosed in a connective tissue capsule. All encapsulated receptors are MECHANORECEPTORS but vary in shape, size, and distribution of the body. TACTILE (MEISSNER'S) CORPUSCLES: located in dermal papillae. Provide discriminative touch LAMELLAR CORPUSCLES: PACINIAN CORPUSCLES: located in the dermis. Respond to pressure/vibration BULBOUS CORPUSCLES: RUFFINI ENDINGS: located in the dermis. sense deep pressure and stretch. THESE 3 PROVIDE PROPRIOCETPITVE INFORMATION: MUSCLE SPINDELS: located in the perimysium. In skeletal muscles. sense muscle stretch and initiate a reflex that resists the stretch. GOLGI TENDON ORGANS: located in tendons. sense tendon stretch. JOINT KINESTHETIC RECEPTORS: in articular capsules. sense stretch of capsule
Describe the components of a reflex arc. What is the importance of a reflex arc?
Reflexes: The spinal cord is a major reflex center. A reflex is a rapid, predictable, automatic response to a change in the environment. Reflexes are the body's principal mechanism for responding to certain changes in the internal or external environment and are used to maintain homeostasis. Reflexes are usually associated with skeletal muscle, but also control such functions as heart rate, respiration, digestion and urination. The reflex arcs that we cover will be somatic spinal reflexes, but you should be aware that you also have cranial reflexes and visceral (autonomic) reflexes. Reflexes can be innate (ex. Pulling your hand back from a hot surface) or learned (ex. Driving a car.) Reflexes can also be modified. The components of a reflex arc: 1. receptor 2. sensory neuron 3. integration center: this varies, the incoming sensory impulse generates the outgoing motor impulse either directly (in which case the integration center is the synapse between the two) or by means of an association neuron. The response can be due to excitation or inhibition. 4. motor neuron 5. effector
Define sensation and perception.
Sensation: awareness of changes in the internal and external environments. Can be at a subconscious level. Your brain knows your body tempt., heart rate, etc. consciously are not aware of these things in general. Perception: conscious interpretation of those stimuli. determines response.
Describe the reflex arcs included in the text. Give their components and function
Stretch reflex: causes contraction of muscle that has suddenly been stretched. It is a feedback system to control muscle length. Reflex arc contains only 2 neurons (and therefore, only one synapse). Receptor: muscle spindle Sensory neuron Motor neuron Effector: extensor An example is the patellar reflex = knee jerk. Pull ligament, stretch quadriceps femoris, extension at knee as quadriceps shortens. This is an ipsilateral reflex (stimulus and response are on same side of body). Other neurons are involved: in addition to sending a signal to the motor neuron to cause extension, the sensory neuron also sends signals through an association neuron to inhibit the flexors. This is reciprocal innervation and conflict is avoided between prime movers and antagonists. The sensory neuron also synapses with neurons that go up to the brain and the brain receives the information about the state of the skeletal muscle. The brain uses this information to coordinate movements and posture. Golgi Tendon reflex: This is also ipsilateral, but the reflex arc contains an association neuron. This reflex gives feedback to control muscle tension. Receptor: in tendon (senses increase in tension) Sensory neuron Association neuron Motor neurons: inhibit the effector and stimulate the antagonist. This will decrease the tension in a muscle to a set level. Flexor and Crossed extensor reflexes: These multisynaptic reflexes always occur together. They cause the withdrawal of a limb from pain and extension of the contralateral limb to maintain balance. (If you step on a tack and lift your left foot, you better put your right one down, or you're going to fall over.) Incoming sensory information is sent into the integration center, signals to contract are sent to all the necessary flexor muscles. All of the muscles that contribute to this reflex are not controlled through the same spinal nerve, so information is sent up and down the spinal cord to adjoining segments and out through the corresponding spinal nerves(intersegmental). At the same time as the association neurons are sending signals to the motor neurons for the ipsilateral flexors, they are also crossing the spinal cord and sending signals to the contralateral extensors
Explain the structure, location and function of: free-nerve endings, Tactile discs, hair follicle receptors, Meissner's corpuscles, Pacinian corpuscles, Ruffini endings, muscle spindles, Golgi tendon organs, and joint kinesthetic receptors.
Tactile corpuscles or Meissner's corpuscles: are small receptors in which a few spiraling sensory terminals are surrounded by Schwann cells and then by a thin egg-shaped connective tissue capsule; found just beneath the epidermis in the dermal papillae and are numerous in sensitive and hairless skin areas such as the nipples. fingertips, and soles of the feet. They are receptors for discriminative touch, and apparently play the same role in sensing light touch in hairless skin that hair follicle receptors do in hairy skin. Lamellar corpuscle also called Pacinian corpuscles: are scattered deep in the dermis, and in subcutaneous tissue underlying the skin. They are mechanoreceptors stimulated by deep pressure, they respond only when the pressure is first applied, and best suited to monitoring vibration of on or off pressure stimulus. The largest corpuscular receptors. Bulbous corpuscles or Ruffin endings: which lie in the dermis, subcutaneous tissues, and joint capsules, contain a spray of receptor endings enclosed by a flattened capsule. They bear a striking resemblance to tendon organs which monitor tendon stretch, and probably play a similar role in other dense connective tissues where they respond to deep and continuous pressure Muscle spindles: are fusiform proprioceptors found throughout the perimysium of a skeletal muscle. Each muscle spindle consists of a bundle of modified skeletal muscle fibers, called intrafusal fibers, enclosed in a connective tissue capsule. Muscle spindles detect muscle stretch and initiate a reflex that resists the stretch Tendon organs: are proprioceptors located in tendons, close to the junction between the skeletal muscle and the tendon. They consist of small bundles of tendon (collagen fibers) enclosed in layered capsule, with sensory terminals oiling between and around the fibers. When muscle contraction stretches the tendon fibers, the resulting compression of the nerve fibers activates the tendon organs. This initiates a reflex that causes the contacting muscle to relax Joint kinesthetic receptors: are proprioceptors that monitor stretch in the articular capsules that enclose synovial joints. This receptor category contains at least four receptor types: lamellar, bulbous, free nerve endings and receptors resembling tendon organs. Together these receptors provide information on joint position and motion. PG 489
List and explain the things that processing at the perceptual level allows.
The ability to identify and appreciate sensations depends on the location of the target neurons in the sensory cortex, not on the nature of the message. For example, pressing on your eyeball activates photoreceptors but what you "see" is light. The exact point in the cortex that is activated always refers to the same "where" regardless of how it is activated, a phenomenon called PROJECTION. Features of sensory perception: Perceptual detection: is the ability to detect that a stimulus has occured. This is the simplest level of perception. As a general rule, inputs from several receptors must be summed for perceptual detection to occur. Magnitude estimation: is the ability to detect how intense the stimulus is. Perceived intensity increases as stimulus intensity increases because of frequency coding Spatial discrimination: allows us to identify the site or pattern of stimulation; a common tool for studying this quality in the laboratoy is the two point discrimanation test. This determines how close together two points on the skin can be and still be perceived as two points rather than as one; this test provides a crude map of the density of tactile receptors in the various regions of the skin. The distance between perceived points varies from less than 5 mm on highly sensitive body area (tip of the tongue) to more than 50 mm on less sensitive areas (the back) Feature abstraction: is the mechanism by which a neuron or circuit is tuned to one feature, or property of a stimulus in preference to others. Sensation usually involves an involves an interplay of several stimulus features. Quality discrimination: is the ability to differentiate the submodalities of a particular sensation. Each sensory modality has several qualities or submodalities Pattern recognition: is the ability to take in the scene around us and recognize a familiar pattern, an unfamiliar one, or one that has special significance for us.
Describe the composition and distribution of the nerves of the cervical, brachial, lumbar and sacral plexuses.
The four plexuses and several of their major nerves: 1)Cervical (C1-5): skin & muscles of the head, neck, upper shoulders and diaphragm (phrenic nerve) 2)Brachial (C4-T2): shoulder & arm a)Axillary: deltoid & teres minor b)Musculocutaneous: flexors arm & forearm (biceps brachii, brachialis) c)Median: forearm flexors (except flexor carpi ulnaris) & pronatord) Radial: posterior arm muscles. Extensors forearm & arm, supinator and brachioradialise) Ulnar: flexor carpi ulnaris, intrinsic hand muscles 3)Lumbar (L1-4): anterolateral abdominal wall, anterior and medial thigh a)femoral: flexors of thigh; quadriceps b)obturator: adductors of leg 4)Sacral (L4-S4): buttock, perineum, leg a) sciatic: thigh extensors and adductor magnus, branches intoi) common fibular: crural musclesii) tibial: sural muscles b) superior gluteal: gluteus mediusc) inferior gluteal: gluteus maximus
Explain the classification of sensory receptors by structure.
The overwhelming majority of sensory receptors belong to the general senses and are simply the modified dendritic endings of sensory neurons. Receptors for the SPECIAL SENSES (vision, hearing, etc) are housed in complex SENSE ORGANS. complex receptors, olfaction and gustation, vision and hearing and equilibrium SIMPLE RECEPTORS OF GENERAL SENSES: widely distributed general sensory receptors are involved in tactile sensation (a mix of touch, pressure, stretch, and vibration), temperature monitoring, and pain as well as the "muscle sense" provided by proprioceptors. One type of receptor can respond to several different kinds of stimuli Subdivided into which the dendrites are contained within a connective tissue capsule(encapsulated) and those that do not have a capsule (unencapsulated)
