biology 105 lecture 11 chapter 9 - napa valley college 11 - sensory...fluid-filled cupulas at the...

Nervous System: Sensory Systems

Biology 105 Lecture 11 Chapter 9

Outline

I. Senses II. Sensory receptors III. Touch IV. Vision V. Hearing and balance VI. Smell

Senses

Major senses: touch, hearing, olfaction (smell), taste, and sight.

All the sensory nerves are routed through the thalamus, except the nerves for olfaction.

Sensory Receptor Cells

Sensory receptors are specialized structures that detect specific stimuli (singular = stimulus).

Sensory receptor cells convert the original stimulus into an electrical response that is transmitted through the nerves.

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

The Central Nervous System

We can sense many different kinds of stimuli 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

Merkel Disks

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

Meissner’s Corpuscles

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

Pacinian Corpuscles

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

Ruffini Corpuscles

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

Thermoreceptors

Thermoreceptors – specialized nerve endings; detect changes in temperature

Vision

Sight is complex!

1. Light enters the eye and is focused… 2. Light has to be transformed into an electrical

signal… 3. That signal then has to be processed.

Vision

Light enters the eye 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

Fovea Optic disk (blind spot)

Optic nerve

Choroid Sclera

Vitreous humor (fills the posterior chamber)

Ciliary body

Cornea

Aqueous humor (fills the anterior chamber)

Sclera

Layers of the Eye – Outer Layer

Sclera: Protects and shapes the eye Provides attachment for muscles

Cornea Allows light to enter

Middle Layer of the Eye

The choroid:

Contains blood vessels that supply nutrients and oxygen. Contains melanin and absorbs light reflected from

the retina.

The ciliary body:

A ring of muscle that functions to control the shape of the lens so that light focuses on the retina.

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.

Table 9.1 (2 of 4)

Inner Layer of the Eye

Contains: Retina Photoreceptors - Rods and Cones Fovea

Inner Layer of the Eye - Retina

The retina contains photoreceptors: Rods Cones – detect color

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

Structures of the Eye

Optic Nerve Fluids: Aqueous humor Vitreous humor

Optic Nerve

The optic nerve: Carries visual information to the brain. Forms a blind spot where it leaves the retina.

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

Retina

Choroid

Sclera

Blind spot

Fluid in the Eye

There are two fluid-filled chambers in the eye: Aqueous humor: clear fluid in the anterior

chamber. Supplies nutrients and oxygen to the cornea

and lens, and removes waste. Creates pressure in the eye to maintain the

shape of the eye. Vitreous humor: jelly-like fluid in the posterior

chamber. Holds retina against the wall of the eye.

The lens can change shape depending on whether you are viewing an object that is nearby or far away.

Focuses the light onto the retina.

Ciliary muscles are attached to the lens by ligaments.

Vision Depends on the Eye!

Table 9.1 (4 of 4)

Photoreceptors

Cones and rods contain pigments that absorb light: Cones work best in bright light and provide color

vision. Rods work in low light situations, but can only

provide black and white vision.

Rods and Cones

Figure 9.9 (2 of 2)

Rod cell

Cone cell

Photoreceptors

When there is no light coming in to the eye, cones and rods release neurotransmitters (note that this is 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.

The information from these cells (called bipolar and ganglion cells) is transmitted to the optic nerve, then to the thalamus, and then to the visual cortex.

Ganglion cell layer

Bipolar cell layer

Retina

Photoreceptor cells

Pigment layer

Choroid

Sclera

Electrical signals

Vitreous humor

(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

Vision

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

Which part of the human eye detects colored light?

Cornea

25% 25%25%25%1. Pupil 2. Rods 3. Cones 4. Cornea

A ring of muscle that functions to change the shape of the lens is the:

ry bod

Sclera

25% 25%25%25%

1. Iris 2. Choroid 3. Ciliary body 4. Sclera

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 amplify the vibrations onto a small place (oval window) on the cochlea.

The cochlea is a fluid-filled, coiled membrane.

The vibrations shake the fluid in the cochlea.

Three Regions of the Ear

1. Outer ear: receiver

2. Middle ear: amplifier

3. Inner ear: transmitter

The Outer Ear

Consists of the:

Pinna – gathers the sound, acts like a funnel.

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

Middle Ear

Consists of the:

Tympanic membrane separates the outer ear from the middle ear: vibrates when sound waves hit it.

Three auditory bones – amplify the vibrations: 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, incus, and stapes.

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

Figure 9.12 (2 of 2)

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 (Eustachian tube)

Outer ear (receiver)

Middle ear (amplifier)

Inner ear (transmitter)

External auditory canal

Vestibule

Cochlea

The cochlea is 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

Tectorial membrane

In the ear, the fluid-filled coiled membrane that is responsible for transforming the vibrations into electrical signals is called the:

Tymphan

ic mem

Staples

lea In

25% 25%25%25%1. Tympanic membrane 2. Stapes 3. Cochlea 4. Incus

The tympanic membrane transmits the vibrations to the ___.

Stapes

l window

25% 25%25%25% 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 the base of the semicircular canals have hair cells that are stimulated when the head moves. Hair cells send messages to the brain.

Balance Depends on the Vestibular Apparatus

Figure 9.16a (1 of 2)

Figure 9.16a (2 of 2)

The Vestibular Apparatus – Static Equilibrium

Otoliths are small chalk-like granules.

When the head is tilted, the otoliths move and stimulate hair cells that send messages to the brain.

Figure 9.16b (1 of 2)

Figure 9.16b (2 of 2)

Smell – Olfaction

Sensory nerves for smell go directly to the cerebral cortex, 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 are very connected.

The tongue has taste buds on it. The taste buds have taste cells (receptor cells) in

Food molecules bind to taste cells and stimulate them. The taste cells send the message to sensory

neurons, which send the message to the brain.

Figure 9.18

Read Chapter 9

What is the function of sensory receptor cells?

What is an example of sensory adaptation?

What are the different types of touch stimuli?

What are the types of sensory receptors in skin, and what type of touch do they detect? You should be able to describe their structure.

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 vision signal travel from the photoreceptors to the brain, and which 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, and are they part of the inner, middle or outer ear? What are their functions? Be able to describe the pathway that sound

waves and vibrations follow through the ear.

How does the ear detect head movement and position?

How do we detect odor? Which 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, dilate, constrict, bipolar cell, ganglion cell, photoreceptors, transmit, amplify, otolith, cupula, taste bud

biology 105 lecture 11 chapter 9 - napa valley college 11 - sensory...fluid-filled cupulas at the...

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