Chapter 21: Somatic Senses & Motor Control

Somatic Sensations: PAIN SENSATIONS

- this sensation serves a protective function by signaling the presence of noxious, tissue-damaging conditions. - this sensation may persist even after its producing stimulus is removed b/c the mediating chemical linger, and b/c nociceptors exhibit very little adaption. *Nociceptors - these are the receptors for pain, and are free nerve endings found in every tissue of the body except the brain. intense thermal, mechanical, or chemical stimuli can activate these receptors.

Somatic; Tactile Sensations: ITCH & TICKLE

-* this sensation results from stimulation of free nerve endings by certain chemicals, such as bradykinin, often b/c of a local inflammatory response -* this sensation is mediated by free nerve endings

Classification of Receptors: EXTEROCEPTORS

- these type of receptors are located at or near the body surface, and are sensitive to stimuli originating outside the body. they provide info about external environment, which convey visual, smell, taste, touch, pressure, vibration, thermal, and pain.

SOMATIC SENSATIONS

- these type of sensations arise from stimulation of sensory receptors embedded in the skin or subcutaneous layer, in mucous membranes of the mouth, vagina, and anus, in muscles, tendons and joints, and in the inner ear. - these sensations are of 4 sensory modalities: * Tactile * Thermal * Pain * Proprioceptive

Somatic; Proprioceptive: MUSCLE SPINDLES

- this consists of slowly adapting sensory nerve endings that wrap around 3-10 specialized muscle fibers. - are interspersed among ordinary skeletal muscle fibers and aligned parallel to them. - their main function is to measure Muscle Length - which is how much muscle is being stretched. *Gamma Motor Neurons - these motor neurons adjust the tension to variations in length of the muscle. *

Tactile Sensations; Touch: TYPE I CUTANEOUS MECHANORECEPTORS (MERKEL DISCS)

- this is a slowly adapting touch receptor - these are saucer shaped, flattened free nerve endings that make contact w/ Merkel cells of stratum basale. - are plentiful in the fingertips, hands, lips, and external genitalia.

Somatic; Tactile Sensations: PRESSURE

- this is a sustained sensation that is felt over a larger area than touch. Occurs w/ deformation of deeper tissues. - receptors that contribute to these sensations include corpuscles of touch, type I mechanoreceptors, and lamellated corpuscles. * Lamellated/Pacinian Corpuscles - are large oval structures made of multilayered connective tissue capsule that encloses a dendrite.

Somatic; Tactile Sensations: TOUCH

- this is generally the result from stimulation of tactile receptors in the skin or subcutaneous layer. - two types of rapidly adapting touch receptors: 1.) Meissner Corpuscles 2.) Hair Root Plexuses - also two types of slowly adapting touch receptors: * Type 1 Cutaneous Mechanroceptors (Merkel Discs) * Type II Cutaneous Mechanoreceptors (Ruffini Corpuscles)

PERCEPTION

- this is the conscious awareness and interpretation of a sensation. - these are integrated in the cerebral cortex. - you see w/ your eyes, hear w/ your ears, and feel pain in an injured part of your body b/c sensory impulses from each part of the body arrive in a specific region of the cerebral cortex, which interprets the sensation as coming from the stimulated sensory receptors.

SENSATION

- this is the conscious or subconscious awareness of changes in the external or internal conditions of the body. - for this to occur, four conditions must be satisfied: 1.) Stimulus - or a change in environment capable of activating certain sensory neurons. 2.) Sensory Receptors - must convert the stimulus to nerve impulses 3.) Conducted - nerve impulses must be conducted along a neural pathway from the sensory receptor to brain. 4.) Integrate - a region of the brain must receive & integrate the nerve impulses, producing a sensation.

Types of Pain: SUPERFICIAL SOMATIC PAIN

- this pain arises from stimulation of receptors in the skin.

Types of Pain: DEEP SOMATIC PAIN

- this pain comes from stimulation of receptors in skeletal muscles, joints, tendons, and fascia.

Pain Sensations: REFERRED PAIN

- this pain is felt in or just deep to the skin that overlies the stimulated organ, or in a surface area far from the stimulated organ.

Types of Pain: VISCERAL PAIN

- this pain results from stimulation of nociceptors in visceral organs.

Somatic; Tactile Sensations: VIBRATION

- this sensation results from rapidly repetitive sensory signals from tactile receptors. - the receptors for this sensation are Corpuscles of touch and Lamellated Corpuscles.

Somatic Sensations: THERMAL SENSATIONS

- have two distinct sensations - coldness & warmth - and are detected by different receptors. *Cold Receptors - located in stratum basale of epidermis. * Warm Receptors - located in dermis

Tactile Sensations; Touch: MEISSNER CORPUSCLES

- is a rapidly adapting touch receptor. - are receptors for fine touch, located in dermal papillae of hairless skin. - is a mass of dendrites enclosed by an egg-shaped capsule of connective tissue. - they generate nerve impulses mainly at the onset of touch

Tactile Sensations; Touch: TYPE II CUTANEOUS MECHANORECEPTORS (RUFFINI CORPUSCLES)

- is a slowly adapting touch receptor. - are elongated, encapsulated receptors located deep in the dermis, and in ligaments and tendons. - are present in the hands and abundant on the soles, they are the most sensitive to stretching that occurs as digits or free limbs are moved.

CLASSIFICATION OF RECEPTORS

- structural & functional characteristics of sensory receptors can be used to group then into different classes: - Microscopic level, sensory receptors may be classified as: * Free Nerve Endings * Encapsulated Nerve Endings - also, another way to group sensory receptors is based on the location of the receptors & the origin of the stimuli that activate them * Exteroceptors * Interoceptors * Proprioceptors

Classification of Sensations

- the senses can be grouped into two classes: 1.) General Senses 2.) Special Senses

Somatic; Pain Sensations: TYPES OF PAIN

- there are two types of pain: 1) Fast Pain - occurs rapidly after a stimulation is applied. also known as acute, sharp, or pricking pain. this pain is not felt in deeper tissues of the body. 2.) Slow Pain - begins a second or more after a stimulus is applied. gradually increases in intensity over a period of several seconds or minutes. can occur both in the skin and in deeper tissues or internal organs.

Somatic; Proprioceptive: TENDON ORGANS

- these are located at the junction of a tendon and a muscle and protect tendons and their associated muscles from damage due to excessive tension. - these consist of a thin capsule of connective tissue that encloses a few tendon fascicles.

Somatic; Proprioceptive: JOINT KINESTHETIC RECEPTORS

- these are present withing and around the articular capsules of synovial joints.

Tactile Sensations; Touch: HAIR ROOT PLEXUSES

- these are rapidly adapting touch receptors found in hairy skin. - they consist of free nerve endings wrapped around hair follicles. - detect movement on the surface of the skin that disturb hairs.

Somatic Sensations: CUTANEOUS SENSATIONS

- these are sensations that arise from stimulating the skin surface. - these are the areas w/ the highest density of somatic sensory receptors, which are the tip of the tongue, the lips, and the fingertips.

Classification of Sensations: GENERAL SENSES

- these particular senses refer to both somatic senses & visceral senses: * Somatic Senses - are tactile sensations (touch, pressure, vibration); thermal sensations (temp); pain sensations, and proprioceptive sensations, which allow perception of both static (nonmoving) positions of limbs & body parts and movements of the limbs and head. * Visceral Senses - these provide info about conditions w/in internal organs.

Classification of Receptors: INTEROCEPTORS

- these receptors are located in blood vessels, visceral organs, and nervous system. They provide info about internal environment, and the impulses they produce usually are not consciously perceived, but occasionally may be felt as pain or pressure.

Classification of Receptors: PROPRIOCEPTORS

- these receptors are located in muscles, tendons, joints, and inner ear. They provide info about body position, muscle length and tension, position and motion of joints, and equilibrium (balance).

Somatic Sensations: PROPRIOCEPTIVE SENSATIONS

- these sensations allow us to know where our head and free limbs are located and how they are moving even if we are not looking at them. - these sensations also allow us to estimate weight of objects in order to determine our muscular effort necessary to lift. *Proprioceptors - proprioceptive sensations arise in these receptors. when embedded in muscles and tendons, it informs us of the degree to which muscles are contracted, amount of tension in tendons, and position of joints.

Somatic Sensations: TACTILE SENSATIONS

- these sensations include touch, pressure, vibration, itch, and tickle. - these type of sensations include * Touch * Pressure & Vibration * Itch & Tickle

Classification of Sensations: SPECIAL SENSES

- these senses include smell, taste, vision, hearing, and equilibrium (balance).

Classification of Receptors: FREE NERVE ENDINGS

- these type of receptors are bare dendrites associated w/ pain, thermal, tickle, itch, and some touch sensations.

Classification of Receptors: ENCAPSULATED NERVE ENDINGS

- these type of receptors are dendrites enclosed in a connective tissue capsule for pressure, vibration, and some touch sensations.