General Senses

General Senses ● Receptors that are dispersed throughout the body. ● Located in the skin, various organs, and joints. Special Senses ● Specialized receptors in the head (eyes, ears, nose, and mouth) Sensory Receptors ● Specialized cells or multicellular structures that gather environmental information and send signals to the brain via sensory (afferent) fibers. Sensation ● A feeling that occurs when the brain becomes aware of sensory impulse. Perception ● An individual’s perspective on a stimulus and how the brain interprets the information. RECEPTOR TYPES Chemoreceptors ● Respond to concentrations. changes in ● ● ● ● Allows a person to pinpoint the region of simulation. Touch sensation Phantom limb pain Hearing adaptation SENSORY ADAPTATION ● Ability to ignore unimportant stimuli by decreasing the response to a repeated or constant stimulus ● Helps prevent sensory overload ● Sensory impulses decrease and may stop. ● Stronger stimulus to reactivate the sensation. ● Helps on focusing on new or changing stimuli rather than constant ones. A. Peripheral Adaptation – Occurs at the level of sensory receptors, which reduce their response over time. ● Example: After putting on a watch, you stop feeling its presence after a while. B. Central Adaptation – Occurs in the CNS when the brain stops processing repetitive signals. ● Example: You get used to a constant background noise, like the hum of an air conditioner. chemical Pain Receptors (nociceptors) ● Respond to chemicals released during tissue damage. Thermoreceptors ● Respond to changes in temperature. Mechanoreceptors ● Respond to mechanical forces (touch, stretch, pressure). Photoreceptors ● Respond to light. SENSORY IMPULSES 1. Receptor Stimulation → Local Change (Receptor Potential) 2. Stronger Stimulus → Stronger Electrical Signal (Graded potential) 3. If the receptor is a Neuron: It may directly trigger an action potential. 4. if the Receptor is NOT a Neuron: It must pass the signal to a neuron first. 5. Peripheral Nerves → CNS → Brain interpretation SENSATIONS AND PERCEPTION Projection ● The brain projects the sensation back to the apparent source. ● Brain’s ability to identify the location of a sensory stimulus by “projecting” the sensation back to its source GENERAL SENSES  Three (3) groups: 1. Exteroceptive senses (exteroceptors) o Senses associated with body surface such as touch, pressure, temperature, and pain 2. Visceroceptive senses (interoceptors) o Senses associated with changes in the viscera such as blood pressure stretching blood vessels and ingestion of a meal. 3. Proprioceptive senses o Senses associated with changes in muscles and tendons such as at joints. TOUCH AND PRESSURE SENSES A. Free Nerve Endings ● Common in epithelial tissues. ● Simplest receptors ● Sense itching B. Tactile (Meissner’s) Corpuscles ● Abundant in hairless portions of skin and lips. ● Detect fine touch; distinguish between two points on the skin. C. Lamellated (Pacinian) Corpuscles ● Common in deeper subcutaneous tissues, tendons, and ligaments. ● Detects heavy pressure and vibrations. Temperature Senses ● Warm Receptors: ○ Ruffini Endings and Free Nerve Endings (C Fibers) ○ Sensitive to temperatures above 25°C (77°F) ○ Unresponsive to temperature above 45°C (113°F) A. TRPV1 – activated by Heat (43°C+), capsaicin and acidity B. TRPV3 – activated by moderate warmth (31-39°C) ● Cold Receptors ○ Krause’s End Bulbs and Free Nerve Endings (A Delta Fibers) ○ Sensitive to temperature between 10°C (50°F) and 20°C (68°F) A. ● TRPM8 - Activated by mild cold (~10– 25°C) and menthol Pain Receptors ○ Nociceptors and Free Nerve Ending (A Delta and C Fibers) ○ Respond to temperatures below 10°C ○ Respond to temperatures above 45°C A. B. TRPV1 - Detects heat pain (~43°C+), capsaicin, and acid TRPA1 - Detects extreme cold (~below 10°C), chemical irritants (mustard oil, wasabi), and mechanical pain o o The trigeminal nerve (cranial nerve V) carries pain sensations from the face and meninges to the brain. Stimulation of the trigeminal nerve pathways contributes to migraines and tension headaches. 3. How Headaches Happen  Headaches are caused by irritation, inflammation, or pressure on these pain-sensitive structures, not the brain itself. Some key mechanisms include: A. Dilation of Blood Vessels - Increases pressure on surrounding tissues. B. Inflammation of the Meninges - Triggers nociceptors in the dura mater. C. Increased Intracranial Pressure - Stretches pain-sensitive structures (e.g., tumors, hydrocephalus). D. Muscle Tension - Tightening of scalp and neck muscles can activate pain pathways.  This explains why brain surgeries can sometimes be performed while a patient is awake— because cutting brain tissue itself does not cause pain, but touching surrounding tissues does. Sense of Pain ● Free Nerve Endings ● Widely Distributed ● Nervous tissue of brain lacks pain receptors ● Adapt very little, if at all ○ Brain doesn’t feel pain. Headaches are caused by pain-sensitive structures that surround the brain. Why Do Free Nerve Endings Adapt Very Little?  Unlike other sensory receptors (e.g., touch or temperature), nociceptors must maintain their response to prolonged injury to ensure the body reacts appropriately to damage.  This is crucial for protecting tissues from further harm. Brain Nervous Tissue Lacks Pain Receptors 1. No Pain Receptors in Brain Tissue  The brain’s neurons and glial cells process sensory information, but they do not have nociceptors.  This means that if the brain itself is cut, stimulated, or even operated on directly, it does not generate pain signals. Visceral Pain - Why does pain feel like it’s coming from another location? ● Only pain receptors in the viscera create sensations when stimulated. ● They react differently to various stimuli. ● Pain receptors are not well localized. ● Pain receptors might feel like it’s coming from another body part. ● Known as referred pain. 2. Pain-Sensitive Structures Around the Brain  Although the brain tissue lacks nociceptors, several nearby structures contain them: A. Meninges (Dura Mater, Arachnoid Mater, Pia Mater) o The dura mater, the outermost meningeal layer, is rich in nociceptors. o Inflammation or stretching of the meninges can lead to severe headaches (e.g., meningitis, migraines). B. Cranial Blood Vessels o The large arteries in the brain (e.g., middle cerebral artery) have nociceptors. o Changes in blood flow, dilation, or inflammation can trigger migraines or vascular headaches. C. Cranial Nerves (Trigeminal, Vagus, etc.) Referred Pain ● May occur due to sensory impulses from two regions following a common nerve pathway to brain. ● Occurs when pain originates from an internal organ ● Visceral pain is poorly localized and only responds to intense stimuli. ● Spinal cord convergence causes the brain to associate organ pain with nearby skin regions. ● Examples: A. Heart Attack → Pain in Left Arm & Jaw 1. The heart receives sensory input through the T1-T5 spinal segments. 2. These segments also receive sensory input from the left arm, chest, and jaw. 3. B. 1. 2. 3. C. 1. 2. 3. D. 1. 2. Since the brain cannot distinguish between signals from the heart and skin, it misinterprets the pain as coming from the left arm or jaw rather than the heart itself. Pain Nerve Pathways Gallbladder Inflammation (Cholecystitis) → Right Shoulder Pain The gallbladder and liver send sensory signals via the phrenic nerve (C3-C5). The phrenic nerve also innervates the diaphragm and shoulder area. As a result, gallbladder irritation can be perceived as pain in the right shoulder or upper back. Kidney Stones → Lower Back, Groin, or Inner Thigh Pain The kidneys are innervated by T10-L1 spinal segments. These segments also supply sensory input to the lower back, abdomen, and groin. This leads to pain that may start in the lower back and radiate to the groin or inner thigh. Appendicitis → Pain Around the Belly Button The appendix sends signals through the T10 spinal segment, which also supplies the umbilical region (belly button area). Early appendicitis pain is felt around the navel before it later localizes to the lower right abdomen as inflammation spreads. Regulation of Pain Impulses ● Thalamus ○ Allows person to be aware of pain ● Cerebral Cortex ○ Judges intensity of pain. ○ Locates source of pain. ○ Produces emotional and motor responses to pain ● Pain Inhibiting Substances ○ Enkephalins – inhibit pain signals, modulate stress-related pain but are depleted in PTSD ○ Serotonin – stabilizes mood, regulates fear and anxiety, affect chronic pain conditions ○ Endorphins – provide pain relief and euphoria, help dull emotional distress, natural stress relievers Regulation of Pain Impulses Neuro trans mitter Role in Physical Pain Role in Emotional Pain Role in Mental Pain (Stress, PTSD, Anxiety) Examples Enke phalin s Block pain signals in the spinal cord and brainstem, reducing pain perception. Provide mild emotional relief by dampening discomfort and distress. Modulate stressinduced pain; low levels are linked to increased pain sensitivity in PTSD. -Reduced pain sensation after an injury -Increased pain tolerance in athletes under stress. Endor phins Act as natural opioids, blocking pain signals and producing analgesia. Promote feelings of well-being and euphoria, reducing emotional distress. Act as natural stress relievers, increasing resilience to mental strain and trauma. -”Runner’s High” after intense exercise -Euphoria after childbirth (natural opioid effect). Serot onin Modulates pain perception, influencing conditions like fibromyalgia and migraines. Stabilizes mood; deficiency is linked to depression and emotional instability. Regulates fear and anxiety; low levels contribute to PTSD and generaliz ed anxiety disorder. -Low serotonin is linked to increased pain sensitivity in migraines Antidepressa nts (SSRIs) enhance serotonin to Free Nerve Endings improve (mechanoreceptors) mood and reduce stress. Muscle Spindles (mechanoreceptors) Proprioception ● Mechanoreceptors ● Send information to spinal cord and CNS about body position and length,and tension muscles. ● Main Kinds of proprioceptors: ○ Pacinian Corpuscles - in joints ○ Muscles Spindles - in skeletal muscles ○ Golgi Tendon Organs - in tendons ● Considered to be stretch receptors Stretch Receptors Visceral Senses ● Receptors in internal organs. ● Provide signals like feeling full after a meal, discomfort from intestinal gas, or the pain indicating a heart attack. Summary of Receptors of the General Senses Type Function Sensation Free Nerve Endings (mechanoreceptors) Detect changes in pressure Touch, pressure Tactile Corpuscles (mechanoreceptors) Detect objects moving over the skin Touch, texture Lamellated Corpuscles (mechanoreceptors) Detect changes in pressure Deep pressure, vibrations, fullness in viscera Free Nerve Endings (thermoreceptors) Detect changes in temperature Heat,, cold Free Nerve Endings (pain receptors) Detect tissue damage Pain Golgi Tendon Organs (mechanoreceptors) Detect stretching of tissues, tissue spasms Visceral pain Detect changes in muscles length None Detect changes in muscles tension None