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”