Nervous System and Sensory Organs

Biology 171 – Lab 12

Lab Activities

• Fetal Pig – Spinal Cord

• Sheep Brain Dissection

• Cow Eye Dissection

• Review for Final

• Central Nervous System (CNS) = Brain and Spinal Cord

• Peripheral Nervous System (PNS) = Nerves

Function:

1) Receive sensory input

2) Perform integration

3) Generate motor outputs

Neurons

Parts: • Cell body

▫ Contains nucleus and organelles

• Dendrites ▫ Receive signal,

transmit to cell body

• Axon ▫ Sends signal to other

cells ▫ Insulated by myelin

sheath

Neurons Types: • Interneuron

▫ Entirely within CNS ▫ Conduct nerve impulses

between parts of the CNS

• Sensory Neuron ▫ Take nerve impulses from

the sensory receptors to the CNS.

• Motor neuron ▫ Takes nerve impulses from

CNS to muscles or glands. ▫ Cause muscles/glands to

contract/secrete

The Spinal Cord

• Gray matter (b)

▫ Cell bodies, unmyelinated fibers

▫ Sensory neurons, motor neurons, short interneurons that connect MN and SN

• White matter (c)

▫ Long myelinated fibers of interneurons, form tracts

▫ Tracts connect the spinal cord to the brain

▫ Superhighway

The Spinal Cord

• Bundle of nervous tissue surrounded by vertebral column

• Main functions:

1) Center for reflex actions

2) Communication between brain and spinal nerves

Surrounded by vertebrae and meninges

• Cerebrospinal fluid in central canal of spinal cord (a)

Reflexes

Sensory receptor Sensory neurons interneurons (spinal cord) Motor neurons

Reflexes • Reflex = involuntary and

predictable response to a stimulus

• Sensory receptor Sensory neurons interneurons (spinal cord) motor neurons

• Consciousness of stimulus lags behind response because information has not reached the brain by the time the reaction occurs.

Brain • Four ventricles: produce cerebrospinal fluid

▫ two lateral in cerebrum

▫ third ventricle in diencephalon (center of brain)

▫ fourth ventricle between cerebrum and pons

Cerebrum

Cerebrum • Right/left hemispheres

• Longitudinal fissure

• Connected via corpus callosum

• Cerebral Cortex

• Grooves called sulci; divide into lobes.

Lobes

• Frontal

▫ Primary motor

▫ Motor speech

Lobes

• Parietal

▫ Primary somatosensory area

▫ Primary taste area

Lobes

• Occipital

▫ Primary visual area

▫ Visual association

Lobes

• Temporal

▫ Primary auditory

▫ Auditory association

Cerebellum

• Motor coordination

• Tree-like pattern of white and dark matter

Brainstem

• Midbrain Relay station for

tracts between the cerebrum and the spinal cord or cerebellum

• Pons Reflex center

• Medulla Reflex center

Diencephalon • Thalamus

▫ Sides and roof of 3rd ventricle

▫ Receives sensor input, integrates info, sends to cerebrum

▫ “Gatekeeper”

• Hypothalamus

▫ Forms floor of 3rd ventricle

▫ Integrating center, regulates homeostasis

Corpus Callosum

Diencephalon

• Pineal Gland

▫ Secretes melatonin

• Pituitary Gland

▫ Secretes hormones

▫ Regulated by hypothalamus

Comparison of Vertebrate Brains

Comparison of Vertebrate Brains

Sense Organs

Eyes, Ears, Skin

Eye Function

• Photoreceptors: sensory receptors sensitive to light

• Generate nerve impulses, pass to brain via optic nerve

Types of Eyes

• Eyespots

▫ Do not form images; allow for animal to detect the direction of light.

▫ Example: planarians

Types of Eyes • Compound Eyes

▫ Composed of individual units called ommatidia

▫ Insects, spiders.

Camera-Type Eyes

• Vertebrates and some molluscs (squid and octopus)

• Convergent Evolution

▫ Trait evolves separately on different lineages.

• Single lens focuses an image onto closely packed photoreceptors (like film)

Parts of the Human Eye

Parts of the Human Eye Three layers: Sclera – fibrous white outer layer, Choroid – middle layer, brown pigments, absorbs stray light rays. Retina – innermost layer, photoreceptors

Retina Choroid Sclera

Sclera

Sclera – fibrous white outer layer, transparent front is called the cornea, the “window to the eye”. Conjunctiva – thin layer of epithelial cells forms a mucus membrane, keeps eye moist. Covers surface of sclera.

Cornea

Sclera

Conjunctivitis – Pink Eye

• Causes:

▫ Viruses (most commonly)

▫ Allergies

▫ Bacteria

▫ Chemicals

• Typically resolves in 3-5 days.

• Prevention: don’t touch eyes!

Choroid Choroid–contains blood vessels and brown pigment to absorb stray light rays. Toward the front of the eye, thickens and becomes: Ciliary body – ring-shaped Iris – muscular diaphragm, regulates size of the opening of the eye. Pupil – opening controlled by iris. Lens – attached to ciliary body by ligaments

Choroid

Ciliary body

Iris

Lens, Compartments, and Fluids Lens – attached to ciliary body by ligaments. Refracts and focuses light rays. Divides the eye into two compartments. Anterior Compartment: between cornea and lens. Filled with aqueous humor, which provides cushion and nutrient/waste transport. Posterior Compartment: behind lens. Filled with vitreous humor, which maintains shape of eye.

Posterior Compartment

Lens

Anterior Compartment

Retina Retina – Contains photoreceptors. Rod cells – sensitive to light, but do not sense color. Cone cells – Require bright light, sensitive to different wavelengths of light (color). Fovea centralis – region of retina where cone cells are densely packed. Sensory fibers form the optic nerve, which takes nerve impulses to the brain.

Fovea Centralis

Retina

Optic Nerve

???

Focusing the Eye – Visual Accommodation

Abnormalities

Nearsighted = can see near Farsighted = can see far Astigmatism = uneven cornea.

Brain Dissection – After cutting

• Find/Identify: ▫ Two lateral ventricles ▫ 3rd and 4th ventricles ▫ Thalamus and

Hypothalamus ▫ Midbrain, pons, medulla

oblongata ▫ Corpus callosum ▫ Cerebrum ▫ Cerebellum – tree pattern

Lab Activities

• Fetal Pig – Spinal Cord

▫ Follow p 116- 119

• Sheep Brain Dissection

▫ Follow p 120 - 124

• Cow Eye Dissection

▫ Follow handout

• Exam Review

Structures to Locate

Spinal Cord (p 116- 119) Brain (p 120 – 124)

• Vertebrae

• Meninges

• White matter

• Grey matter

•Cerebrum

▫ Frontal, Parietal, Temporal, Occipital lobes

•Sulci

•Longitudinal Fissure

•Lateral Ventricles (2)

•3rd and 4th Ventricles

•Midbrain

•Pons

•Medulla Oblongata

•Corpus callosum

•Cerebellum

Cow Eye Dissection

Instructions Structures to Find

• www.exploratorium.edu/learning_studio/cow_eye/coweye.pdf‎

• Cut around Sclera

• Cornea in front half

• Sclera

• Cornea

• Pupil

• Choroid

• Ciliary body

• Iris

• Retina

• Lens

• Aqueous humour

• Vitreous humour

• Optic Nerve

Course Evaluations

• ONLINE this year!!

• https://csi.mce.im/

• Use CIX login and password

• MUST DO BEFORE DEC 15 11:59 PM