Lecture12 2 13
-
Upload
maya-phillips -
Category
Health & Medicine
-
view
116 -
download
3
description
Transcript of Lecture12 2 13
Week 11: Brain: functions of the cerebrum General Senses; Motor and sensory relays to & from
brain Eye and vision
****REVIEW SESSION???
Lab 10: special senses - eye and ear; tactile receptors; reflexes
Today- Quiz on Lab 9
Lecture Reading: Martini: pp 466-477, 536-545, 424-428, 495-514, 555-574
Lab Reading: Martini: pp 555-563, 574-588, 499-501, 436-43 AM: 88-89,93,104-6
Figure 14–15a
Regions and Functions of the Cerebral Cortex
Central sulcus separates motor and sensory areas
Sensation• The arriving information from senses
Perception
• Conscious awareness of a sensation
General Senses
• Describe our sensitivity to:– temperature– pain– touch– pressure– vibration– proprioception
Special Senses
• Olfaction (smell)• Vision (sight)• Gustation (taste)• Equilibrium (balance)• Hearing
Figure 15–2
Receptive Field• Area monitored by a single receptor cell• The larger the receptive field, the more difficult to
localize a stimulus
Classification Of Sensory Receptors
• Defined by the nature of the stimulus that excites them:
– nociceptors (pain)
– thermoreceptors (temperature)
– mechanoreceptors (physical distortion)
– chemoreceptors (chemical concentration)
Pain Receptors• also called nociceptors
• common in:– superficial skin– joint capsules– periostea of bones– around the walls of blood vessels
• Free nerve endings with large receptive fields
• May be sensitive to:– extremes of temperature– mechanical damage– dissolved chemicals, (eg., released by injured cells)
Figure 15–2
Myelinated Type A Fibers• Carry sensations of fast pain, or prickling pain, such as
that caused by an injection or a deep cut
• Sensations often trigger somatic reflexes
• Relayed to the primary sensory cortex and receive conscious attention
Type C Fibers
• Carry sensations of slow pain, or burning and aching pain
• Cause a generalized activation of the reticular formation and thalamus
• aware of the pain but only have a general idea of the area affected
Reticular FormationThalamus
Thermoreceptors• Also called temperature receptors
• Free nerve endings located in:– the dermis– skeletal muscles– the liver– the hypothalamus
• Sent to:– the reticular formation– the thalamus– the primary sensory cortex (to a lesser extent)
Mechanoreceptors
• Sensitive to stimuli that distort cell membrane
• Contain mechanically regulated ion channels whose gates open or close in response to:– stretching– compression– twisting– or other distortions of the membrane
• Tactile receptors: – sensations of touch, pressure, and vibration
3 Classes of Mechanoreceptors
• Baroreceptors: – detect pressure changes in the walls of blood
vessels and parts of digestive, reproductive, and urinary tracts
• Proprioceptors: – monitor the positions of joints and muscles – eg., muscle spindles
Fine Touch and Pressure Receptors • extremely sensitive• narrow receptive field• provide detailed information about:
– exact location– shape– size– texture– movement
Crude Touch and Pressure Receptors
• have relatively large receptive fields• provide poor localization and little info about
stimulus
Tactile Receptors
Figure 15–3
Figure 15–3a
Tactile Receptors in the Skin
• Free nerve endings: – sensitive to touch and pressure– situated between epidermal cells– tonic receptors with small receptive
fieldsTonic= always active
• Root hair plexus nerve endings:– monitor distortions and movements
across the body surface – adapt rapidly (will “turn off” after
stimulated), best at detecting initial contact and subsequent movements
Figure 15–3c
• Merkel’s discs:– fine touch and pressure receptors– extremely sensitive; tonic – very small receptive fields
Tactile Receptors in the Skin
• Meissner’s corpuscles :– fine touch, pressure, and low-
frequency vibration– Rapidly adapting– abundant in the eyelids, lips,
fingertips, nipples, and external genitalia
Figure 15–3e
• Pacinian corpuscles: – sensitive to deep pressure– rapidly-adapting– sensitive to pulsing or high-
frequency vibration
Tactile Receptors in the Skin
• Ruffini corpuscles:– sensitive to pressure and distortion
of the skin– Located in deep dermis– tonic receptors; little if any
adaptation
Chemoreceptors
• Respond to water-soluble and lipid-soluble substances
• Located in carotid arteries and aorta
• Monitor Ph, carbon dioxide, and oxygen levels in blood
Figure 13–5b
Anatomy of the Spinal Cord
• Gray matter:– neuron cell
bodies, neuroglia, unmyelinated axons
• White matter:– ascending and descending axons – columns of axon bundles with specific functions
Organization of White Matter
• 3 “white columns” (funiculi) on each side of spinal cord: – posterior– anterior– lateral
Organization of Sensory Pathways
First-Order Neuron
Third-Order Neuron
Second-Order Neuron
First-Order Neuron • Sensory neuron
• Cell body located in dorsal root ganglion or cranial nerve ganglion
Second-Order Neuron
• Sensory neuron synapses on an interneuron in the CNS
• May be located in the spinal cord or brain stem
• Axon crosses!
Third-Order Neuron
• second-order neuron synapses on a third-order neuron in the thalamus
• Right thalamus and primary cortex receive sensory information from left side of body and vice versa.
• “reaches our awareness”