Nervous System – Sensory Systems Biol 105 Lecture 11 Chapter 9.

Nervous System – Sensory Systems

Biol 105

Lecture 11

Chapter 9

1. Depolarization is caused by ______ ions entering or leaving (which one) the axon

1. The gap in between two neurons is called the ________.

2. What is the name for the chemicals that are held in vesicles and released from one neuron, and bind to receptors of the next neuron?

3. What part of the autonomic nervous system stimulates digestion?

4. What is the thin outer layer of the cerebrum where most of the higher thinking and processing takes place called

5. The part of the brain that processes sensory information (except smell) is called the ______.

Concepts to Know:

Outline

I. Senses

II. Sensory receptors

III. Touch

IV. Vision

V. Hearing and balance

VI. Smell

Senses

Major senses – touch, hearing, smelling, taste, and seeing.

All the sensory nerves are routed through the thalamus except the nerves for smell.

Sensory receptor cells

Sensory receptors are specialized structures that detect stimuli (stimulus)

Sensory receptor cells change the stimulation into an electrical response that is transmitted through the nerves

If a sensory receptor is continuously stimulated, it will stop responding = sensory adaptation

12.2 The Central Nervous System

We can sense different things through touch:

Thermal Tactile Pain Vibration

Figure 9.2 Sense receptors of the skin

Types of receptors in the skin

Free nerve endings Merkel disks Meissner’s corpuscles Pacinian corpuscles Ruffini corpuscles Thermoreceptors

Free Nerve Endings

Free nerve endings – tips of dendrites of sensory neurons (free nerve endings may be wrapped around hair), detect touch and pain

Figure 9.2 Free nerve endings

Merkel Disks

Merkel disks – comprised of free nerve endings and Merkel cells, detect touch

Merkel disk

Meissner’s corpuscles

Meissner’s corpuscles – encapsulated nerve endings - detect light touch, tell us exactly where we were touched

Meissners corpuscle

Pacinian corpuscles

Pacinian corpuscles – layers of tissues surround the nerve ending, detects pressure when first applied, important in sensing vibration

Pacinian corpuscle

Ruffini corpuscles

Ruffini corpuscles – encapsulated nerve endings in deep layers that respond to continuous pressure

Ruffini corpuscle

Thermoreceptors

Thermoreceptors – specialized nerve endings, detects changes in temperature.

Vision

Sight is complex:

Light enters the eye, it is focused, then the light has to be transformed into it into an electrical signal that then has to be processed.

Vision

Light enters through the cornea

The lens focuses it to the back of the eye

The retina is a layer at the back of the eye where light is transformed into electrical signals

Retina

FoveaOptic disk(blind spot)

Optic nerve

Choroid

Sclera

Vitreous humor(fills the posteriorchamber)

Ciliary body

Cornea

Aqueous humor(fills the anteriorchamber)

Sclera

Layers of the Eye – Outer layer

The sclera Protects and shapes the eye Provides attachment for muscles

The cornea

Allows light to enter

Outer Layer of Eye

Table 9.1 (1 of 4)

Middle Layer of Eye

The choroid

Contains blood vessels that supply nutrients and oxygen.

Contains melanin, absorbs light reflected from the retina

The ciliary body

A ring of muscle that functions to focus the lens on the retina

Middle Layer of Eye

The iris

The colored portion of the eye Contains smooth muscle that dilates or constricts

to regulate the amount of light entering the eye

The pupil

The opening in the center of the iris that lets light into the eye

Middle Layer of the Eye

Table 9.1 (2 of 4)

Inner Layer of Eye

Contains: Retina Photoreceptors - Rods and Cones Fovea

Inner Layer of Eye - Retina

The retina contains photoreceptors Rods Cones – detect color

The fovea is a pit in the retina with a high concentration of cones

Vision Depends on the Eye

Table 9.1 (3 of 4)

Structures of the Eye

Optic Nerve Fluid

Aqueous humor Vitreous humor

Optic Nerve

The optic nerve

Carries visual information to the brain Forms a blind spot where it leaves the retina

Fluid in the Eye

There are two fluid filled chambers in the eye

Vitreous humor – jelly like fluid in posterior chamber. Holds retina against the wall of the eye

Aqueous humor – clear fluid in anterior chamber. Supplies nutrients and oxygen to cornea and lens, removes the waste. Creates pressure in eye to maintain shape of eye.

The lens can change shape to focus on near and far objects.

Focuses the light onto the retina

Ciliary muscles are attached to lens by ligaments

Vision Depends on the Eye

Table 9.1 (4 of 4)

Photoreceptors

Cones and Rods have pigments that absorb

Cones work best in bright light and provide color vision

Rods work in low light situations but can only provide black and white vision

Photoreceptors

The photoreceptors (rods and cones) have pigments that absorb light

When there is no light coming in, they are releasing neurotransmitters (opposite of most receptors)

When they absorb light they stop releasing neurotransmitters

Photoreceptors

The neurotransmitters are inhibitory

When the neurotransmitters diminish, cells that process the information are stimulated

This information from these cells (bipolar and ganglion cells) is transmitted to the optic nerve to the thalamus to the visual cortex

(a) Light enters the left eye and strikes the retina.

Retina

Choroid

Sclera

Blind spot

Ganglioncell layer

Bipolarcell layer

Retina

Photoreceptorcells

Pigment layer

Choroid

Sclera

Electricalsignals

Vitreoushumor

(c) The axons of the ganglion cells leave the eye at the blind spot, carrying nerve impulses to the brain (viewed from below) by means of the optic nerve.

Retina

Optic nerve

Visual cortex

Rods and Cones

Figure 9.9 (2 of 2)

Rod cell

Cone cell

Which part of the human eye detects colored light?

1. Pupil

2. Rods

3. Cones

4. Cornea

A ring of muscle that functions to focus the lens on the retina is the:

1. Iris

2. Choroid

3. Ciliary body

4. Sclera

Figure 9.10 A standard test for color blindness

Vision

Vision is much more complicated because these signals have to be processed into a 3-D image

Hearing

Sound enters the ear canal and hits the tympanic membrane (ear drum).

The tympanic membrane vibrates.

This causes small bones in the ear to vibrate.

These bones focus and amplifies the vibrations onto a small place (oval window) on the cochlea.

The cochlea is a fluid filled coiled membrane.

The vibrations shakes the fluid in the cochlea

Three regions of the ear

Outer ear – the receiver

The middle ear – the amplifier

The inner ear – the transmitter

Three Regions of the Ear

Figure 9.12 (1 of 2)

Outerear(receiver)

Middleear(amplifier)

Innerear(transmitter)

The Outer Ear

Consists of the:

Pinna – gathers the sound, acts like a funnel

External auditory canal – brings the sound from pinna to the tympanic membrane

Middle Ear

Consists of the:

The tympanic membrane separates the outer ear from the middle ear, vibrates when sound waves hit it.

Three auditory bones – amplify the vibration Malleus Incus Stapes

Auditory tube (eustachian tube) – equalizes pressure between outer and middle ear

Middle Ear

The tympanic membrane vibrates when sound waves hit it and transmits the vibration to the malleus

The vibrations are amplified by the three bones and transmitted to the oval window

Parts of the Inner Ear

Oval window – transmits sound from the stapes to the fluid in the cochlea

Round window – relieves pressure

Cochlea – contains the receptor cells that transform the signal from vibration to an electrochemical signal to the neurons.

Vestibular apparatus – monitors position of the head

Hearing Depends on the Ear

The pinna gathers sound and funnels it into the external auditory canal to the tympanic membrane (eardrum).

The eardrum vibrates synchronously with sound waves, causing the bones of the middle ear to move.

The three bones of the middle ear amplify the pressure waves and convey the vibrations of the eardrum to the inner ear.

The cochlea converts pressure waves to neural messages that are sent to the brain for interpretation as sound.

Malleus(hammer)

Incus(anvil)

Stapes(stirrup)

Semicircular canals

Vestibular apparatus:

Auditory nerve

Cochlea

Oval window

Eardrum(tympanic membrane)

Round window

Auditory tube(Eustachiantube)

Outer ear(receiver)

Middle ear(amplifier)

Inner ear(transmitter)

External auditory canal

Vestibule

Cochlea

It is in the cochlea where vibrations are transformed into electrical signals that can be sent by neurons

When the fluid in the cochlea moves, it moves small “hair cells” against a membrane. This allows ion channels to open

This leads to the release of neurotransmitters, which trigger the neuron to send the message

Hair cell

Tectorialmembrane

In the ear, the fluid filled coiled membrane that is responsible transforming the vibrations into electrical signals. This structure is:

1. Tymphanic membrane

2. Staples

3. Cochlea

4. Incus

The tympanic membrane transmits the vibration to the ___.

Stapes Malleus Incus Oval window

The Vestibular Apparatus

Balance depends on the vestibular apparatus of the inner ear

The vestibular apparatus is a fluid-filled maze of chambers and canals within the inner ear

The Vestibular Apparatus - Dynamic equilibrium

Fluid filled cupulas at base of the semicircular canals have hair cells that are stimulated when head moves. Hair cells send message to the brain.

The Vestibular Apparatus - Static equilibrium

Otoliths are small chalk like granules

When head is tilted the otoliths move and stimulate hair cells that send message to the brain

Balance Depends on the Vestibular Apparatus

Figure 9.16a (1 of 2)

Balance Depends on the Vestibular Apparatus

Figure 9.16a (2 of 2)

Figure 9.16b (1 of 2)

Figure 9.16b (2 of 2)

Smell - olfaction

Sensory nerves for smell go directly to the cerebral cortex and to the amygdala and the hypothalamus.

They do not pass through the thalamus

Smell - olfaction

Odor molecules bind to the receptors in the cilia of olfactory receptor cells

The receptor cells send the message to the neurons in the olfactory bulb which carry the message to the brain.

Figure 9.17 Sense of Smell

Taste and smell is very connected.

The tongue has taste buds on them

The taste buds have taste cells (receptor cells) in them

Food molecules bind to taste cells and stimulate them. The taste cells send the messages to the sensory neurons which send the message to the brain.

Smell and Taste

Figure 9.18

Read Chapter 6

What is the function of sensory receptor cells?

What is an example of sensory adaptation?

What are the types of senses of touch?

What are the types of sensory receptors in skin, what type of touch do they detect, be able to describe them?

Important Concepts

What are all of the layers and structures (including the fluids) of the eye and what are their functions?

What is the blind spot?

How does the signal travel from the photoreceptors to the brain, what part of the brain receives the signal? Be able to describe in detail this process, including the cells that transmit the messages.

Important Concepts

What are all the parts of the ear, are they part of the inner, middle or outer ear, and what is their functions? What is the path of sound waves and vibrations through the ear

How does the ear detect head movement and position?

How do we detect odor? What part of the brain receives the signal? Where are olfactory receptors found?

How do we detect tastes? What structures are responsible for taste?

Important Concepts

Definitions

stimuli (stimulus), sensory adaptation, dilates, constrict, bipolar cells, ganglion cells, photoreceptors, transmits, amplifies, otoliths, cupula, taste buds,

Nervous System – Sensory Systems Biol 105 Lecture 11 Chapter 9.

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