1. The Special Senses: Sensory, Motor & Integrative Systems

2. Sensation
Conscious and subconscious awareness of changes in the external or internal environment.
Components of sensation: Stimulation of the sensory receptor → transduction of the stimulus → generation of nerve impulses → integration of sensory input.

3. Classification of Sensory Receptors
General senses: somatic and visceral.
Somatic- tactile, thermal, pain and proprioceptive sensations.
Visceral- provide information about conditions within internal organs.
Special senses- smell, taste, vision, hearing and equilibrium or balance.

4. Types of Sensory Receptors
Free nerve endings: pain and thermoreceptors.
Encapsulated nerve endings: pacinian corpuscles.
Separate cells: hair cells, photoreceptors and gustatory receptor cells.

5. Generator Potential and Receptor Potential
Generator potential is produced by free nerve endings, encapsulated nerve endings, and olfactory receptors. When it reaches a threshold, it triggers one or more nerve impulses in the axon of a first-order sensory neuron.
Receptor potential triggers the release of neurotransmitter → postsynaptic potential → action potential.

6. Sensory Receptors and their Relation-ship to First-Order Sensory Neurons

7. Classification of Sensory Receptors Based on the Location
Exteroceptors
Interoceptors
Proprioceptors

8. Classification of Sensory Receptors based on the type of Stimulus
Mechanoreceptors
Thermoreceptors
Nociceptors
Photoreceptors
Chemoreceptors
Osmoreceptors

9. Adaptation of Sensory Receptors
Rapidly adapting receptors: receptors that detect pressure, touch and smell.
Slowly adapting receptors: receptors that detect pain, body position, and chemical composition of the blood.

10. Somatic Sensations
Sensory receptors in the skin (cutaneous sensations), muscles, tendons and joints and in the inner ear.
Uneven distribution of receptors.
Four modalities: tactile, thermal, pain and proprioceptive.

11. Sensory Receptors in the Skin

12. Tactile Sensations
Include touch, pressure, vibration, itch and tickle.
Tactile receptors in the skin are Meissner corpuscles, hair root plexuses, Merkel discs, Ruffini corpuscles, pacinian corpuscles, and free nerve endings.

13. Meissner Corpuscles or Corpuscles of Touch
Egg-shaped mass of dendrites enclosed by a capsule of connective tissue.
Rapidly adapting receptors.
Found in the dermal papillae of hairless skin such as in the fingertips, hands, eyelids, tip of the tongue, lips, nipples, soles, clitoris, and tip of the penis.

14. Hair Root Plexuses
Rapidly adapting touch receptors found in the hairy skin.
Free nerve endings wrapped around hair follicles.
Detect movements on the skin surface that disturb hairs.

15. Merkel Discs or Tactile Discs
Also known as type I cutaneous mechanoreceptors.
Slowly adapting touch receptors.
Saucer-shaped, flattened free nerve endings.
Found in the fingertips, hands, lips, and external genitalia.

16. Ruffini Corpuscles Also called as type II cutaneous mechanoreceptors.
Elongated, encapsulated receptors.
Located deep in the dermis and in ligaments and tendons.
Found in the hands, and soles.

17. Pacinian or Lamellated Corpuscles
Large oval structure composed of a multilayered connective tissue capsule that encloses a dendrite.
Fast adapting receptors.
Found around joints, tendons, and muscles; in the periosteum, mammary glands, external genitalia, pancreas and urinary bladder.

18. Thermal Sensations Thermoreceptors are free nerve endings.
Two distinct thermal sensations:
cold receptors-
warm receptors-

19. Pain Sensations Protective. Sensory receptors are nociceptors.
Free nerve endings.
Two types of pain: fast and slow.
Fast pain: acute, sharp or pricking pain.
Slow pain: chronic, burning, aching or throbbing pain.

20. Referred Pain
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.

21. Distribution of Referred Pain

22. Proprioceptive Sensations
Receptors are called proprioceptors.
Slow adaptation.
Weight discrimination.
Three types: muscle spindles, tendon organs and joint kinesthetic receptors.

23. Muscle Spindles
Interspersed among most skeletal muscle fibers and aligned parallel to them.
Measure muscle stretching.
Consists of intrafusal muscle fibers- specialized muscle fibers with sensory nerve endings and motor neurons called gamma motor neurons.
Extrafusal muscle fibers- surrounding muscle fibers supplied by alpha motor neurons.

24. A Muscle Spindle and a Tendon Organ

25. Tendon Organs Located at the junction of a tendon and a muscle.
Protect tendons and their associated muscles from damage due to excessive tension.
Consists of a thin capsule of connective tissue that encloses a few tendon fascicles.

26. Joint Kinesthetic Receptors
Found within or around the articular capsules of synovial joints.
Free nerve endings and Ruffini corpuscles in the capsules of joints respond to pressure.
Pacinian corpuscles respond to acceleration and deceleration of joints during movement.

27. Somatic Sensory Pathways
First-order neuron(somatic receptor to the brain stem/spinal cord)
→ second order neuron(brain stem/spinal cord too the thalamus; decussate)
→ third-order neuron(thalamus to the primary somatosensory area of the cortex).

28. Major Somatic Sensory Pathways
The posterior column-medial lemniscus pathway.
The anterolateral (spinothalamic) pathway.
The trigeminothalamic pathway.
The anterior and posterior spinocerebellar pathway.

29. The 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.

30. The 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.

31. Trigeminothalamic Pathway
Conveys nerve impulses for most somatic sensations from the face, nasal cavity, oral cavity and teeth to the cerebral cortex.

32. Mapping of the Primary Somatosensory Area
Mapping of the postcentral gyrus.
Size of the cortical region representing a body part depends on the sensory impulses received from that part.

33. Somatic Motor Pathways
Upper motor neurons → lower motor neurons → skeletal muscles.
Neural circuits involving basal ganglia and cerebellum regulate activity of the upper motor neurons.

34. Organization of the Upper Motor Neuron Pathways
Direct motor pathway- originates in the cerebral cortex.
Corticospinal pathway: to the limbs and trunk.
Corticobulbar pathway: to the head.
Indirect motor pathway- originates in the brain stem.

35. Mapping of the Motor Areas
Located in the precentral gyrus of the frontal lobe.
More cortical area is devoted to those muscles involved in skilled, complex or delicate movements.

36. The Corticospinal Pathways

37. The Corticobulbar Pathway

38. Indirect or Extrapyramidal Pathways
Originate in the brain stem. Include:
Rubrospinal tract
Tectospinal tract
Vestibulospinal tract
Reticulospinal tract

39. Modulation of Movement from the Cerebellum
The cerebellum coordinates and smoothes contractions of skeletal muscles during skilled movements and helps maintain posture and balance.

40. Sagittal
plane
Motor areas of
cerebral cortex
Corrective
feedback
Pons
Direct pathways
Indirect pathways
Signals to lower
motor neurons
Sagittal section through brain and spinal cord
Sensory signals from
proprioceptors in muscles
and joints, vestibular
apparatus, and eyes
Cortex of
cerebellum 1 2 4 3
Thalamus
Motor centers in
brainstem
Pontine nuclei
Sagittal
plane
Motor areas of
cerebral cortex
Corrective
feedback
Pons
Direct pathways
Indirect pathways
Signals to lower
motor neurons
Sagittal section through brain and spinal cord
Sensory signals from
proprioceptors in muscles
and joints, vestibular
apparatus, and eyes
Cortex of
cerebellum 1 2 3
Thalamus
Motor centers in
brainstem
Pontine nuclei
Sagittal
plane
Motor areas of
cerebral cortex
Corrective
feedback
Pons
Direct pathways
Indirect pathways
Signals to lower
motor neurons
Sagittal section through brain and spinal cord
Sensory signals from
proprioceptors in muscles
and joints, vestibular
apparatus, and eyes
Cortex of
cerebellum 1 2
Thalamus
Motor centers in
brainstem
Pontine nuclei
Sagittal
plane
Motor areas of
cerebral cortex
Thalamus
Corrective
feedback
Motor centers in
brainstem
Pons
Pontine nuclei
Direct pathways
Indirect pathways
Signals to lower
motor neurons
Sagittal section through brain and spinal cord
Sensory signals from
proprioceptors in muscles
and joints, vestibular
apparatus, and eyes
Cortex of
cerebellum 1

41. Integrative Functions of the Cerebrum
Wakefulness and sleep-
Learning and memory-

42. The role of Reticular Activating System (RAS) in Awakening
Consists of neurons whose axons project from the reticular formation through the thalamus to the cerebral cortex.
Increased activity of the RAS causes awakening from sleep (arousal).

43. Sleep A state of altered consciousness.
Two components: non-rapid eye movement (NREM) sleep and rapid eye movement (REM) sleep.
NREM sleep consists of four stages:
Stage 1-
Stage 2-
Stage 3-
Stage 4-

44. Learning and Memory
Learning is the ability to acquire new information or skills through instruction or experience.
Memory is the process by which information acquired through learning is stored and retrieved.

45. Memory Types Immediate memory- recall for a few seconds.
Short-term memory- temporary ability to recall.
Long-term memory- more permanent.
Memory consolidation.

46. Olfactory Sensations: Smell
The receptors for olfaction, which are bipolar neurons, are in the nasal epithelium in the superior portion of the nasal cavity.
Substances to be smelled must be volatile, water-soluble, and lipid-soluble.
In olfactory reception, a generator potential develops and triggers one or more nerve impulses.
Adaptation to odors occurs quickly and the threshold of smell is low; only a few molecules of certain substances need be present in air to be smelled.
Olfactory receptors convey nerve impulses to olfactory (I) nerves, olfactory bulb, olfactory tracts, and the cerebral (perpyriform) cortex and the limbic system.

47. Gustatory Sensations: Taste
The receptors for gustation, the gustatory receptor cells, are located in taste buds.
Substances to be tasted must be in solution in saliva.
Receptor potentials developed in gustatory hairs cause the release of neurotransmitter which gives rise to nerve impulses.
The five primary tastes are: sour, salty, bitter, sweet and umami (Japanese for “meaty/brothy”).
Adaptation to taste occurs quickly, the threshold varies with the taste involved.
Gustatory receptor cells convey nerve impulses to cranial nerves V, VII, IX and X, the medulla, the thalamus, and the parietal lobe of the cerebral cortex.

48. Visual Sensations: Eye Physicians
The study of the structure, function and diseases of the eye is known as ophthalmology; a physician who specializes in diagnosis and treatment of eye disorders with drugs, surgery, and corrective lenses is known as an ophthalmologist.
An optometrist is a specialist with a degree in optometry who is licensed to examine and test the eyes and treat visual defects by prescribing corrective lenses.
An optician is a technician (not a doctor) who fits, adjusts, and dispenses corrective lenses prescribed by an ophthalmologist or optometrist.

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