Lab 10: Central Nervous System

What are neurons?

Neurons are specialized cells of the nervous system

Functions of neurons

Communicate through electrical and chemical signals — electrical signals travel through a neuron and trigger the release of neurotransmitters at the synapse

Parts of a neuron

soma, dendrites, axon

cell body (soma)

Contains the nucleus and the cell’s cytoplasm. It is attached to one or more dendrites and one axon. Specialized rough ER called Nissl bodies produces proteins involved in nerve regeneration and growth

dendrites

Short, highly branched extensions that receive signals and carry them toward the cell body

axons

Begins at the axon hillock and carries electrical signals away from the cell body. It branches into axon terminals

axon terminals/presynaptic terminals

Release neurotransmitters into the synapse

myelin

Insulates the axon and increases the speed of signal conduction

nodes of Ranvier

gaps in the myelin

synapse

The point where neurotransmitters are released to communicate with another cell

gray matter

Contains neuron cell bodies, dendrites, synapses, and some unmyelinated axons; it is involved in processing information

white matter

Contains mostly myelinated axons. Myelin makes it appear lighter and helps signals travel faster

what does white matter form?

White matter forms ascending and descending tracts

Matter of the brain:

gray matter is on the outside and white matter is on the inside

Matter of the spinal cord:

gray matter is on the inside and white matter surrounds it on the outside

Ascending tracts carry . . .

sensory information toward the brain

Descending tracts carry . . .

motor commands away from the brain

functional classification of neurons

sensory neurons, interneurons, and motor nuerons

sensory (afferent) neurons

Carry information from sensory receptors toward the CNS; afferent arrives

interneurons (association neurons)

Located entirely within the CNS; process information and connect sensory neurons to motor neurons

motor (efferent) neurons

Carry commands away from the CNS to activate muscles or glands; efferent exits

pathway of neuron

sensory receptor → afferent neuron → CNS/interneuron → efferent neuron → muscle or gland

meninges

three protective layers of membrane that cover and support the brain and spinal cord in the central nervous system

layers of the meninges

dura mater, arachnoid layer, and pia mater

dura mater

• Outermost layer

• made of fibrous connective tissue

• tightly connected to the periosteum inside the skull and to the brain

• The subdural space is the site of subdural hematomas

arachnoid layer

• Cobweb-like middle layer

• The subarachnoid space contains circulating cerebrospinal fluid (CSF)

• Arachnoid granulations project into the sagittal sinus and allow CSF to drain into the circulatory system

pia mater

• Innermost layer

• adheres directly to the brain

• It cannot be seen with the naked eye

• Meningitis is an infection of the meninges and usually affects the pia or arachnoid layers

order of the layers of the meninges from superficial to deep:

dura mater → arachnoid mater → pia mater

spinal cord protection

vertebra → epidural space → dura → arachnoid → subarachnoid space → pia → spinal cord

cerebrum

the largest and uppermost part of the human brain, making up about 80% of its total mass; It manages higher-level functions like conscious thought, movement, language, and sensory processing

parts of the cerebrum

gyri, sulci, fissures, longitudinal cerebral fissure; central sulcus; precentral gyrus; postcentral gyrus, and lateral sulcus

gyri

Ridges or raised folds on the cerebral surface

sulci

Shallow grooves between gyri

fissures

Deeper grooves

longitudinal cerebral fissure

Separates the left and right cerebral hemispheres

central sulcus

Separates the frontal and parietal lobes; it may be difficult to see on sheep brains

postcentral gyrus

Contains the primary motor cortex

postcentral gyrus

Contains the primary somatosensory cortex

lateral sulcus

Also called the temporal sulcus; it borders the temporal lobe

frontal lobe

• involved in intellect, abstract reasoning, language, and motor control

• The primary motor cortex is in the precentral gyrus

• The premotor area is anterior to the primary motor area and helps control it

• Broca’s area is on the left side

parietal lobe

• Contains the primary somatosensory cortex and sensory association areas

• It processes sensory input and spatial information

• The primary somatosensory cortex is in the postcentral gyrus

• Wernicke’s area is usually on the left, near the temporal/parietal region

occipital lobe

Contains the primary visual cortex and visual association area; it is the visual processing center at the back of the brain

temporal lobe

• Contains the primary auditory cortex and auditory association area

• involved in hearing, language comprehension, and memory

• Wernicke’s area is usually in the left hemisphere

insula

• A deep cortical region hidden beneath the frontal and temporal lobes

• The temporal lobe must be pulled aside to see it

• Associated with balance, body awareness, emotional regulation, internal sensations, and addictive behaviors/cravings

functional regions of the cerebrum

primary motor cortex, premotor area, primary somatosensory cortex, broca’s area, wernicke’s area, visual cortex and visual association area, auditory cortex and auditory association area, association areas

Primary motor (somatomotor) cortex

precentral gyrus; sends commands to muscles

Premotor area

anterior to the primary motor cortex; helps control movement

Primary somatosensory cortex

postcentral gyrus; receives sensory input from the skin and muscles

Broca’s area

• left frontal lobe; speech production

• Broca’s aphasia involves difficulty forming words and sentences (broken speech)

Wernicke’s area

language comprehension; damage results in inability to understand sentences/language

Visual cortex and visual association area

occipital lobe

Auditory cortex and auditory association area

temporal lobe

Association areas

adjacent to somatosensory, visual, and auditory areas; help interpret/integrate information

Contralateral control

Each hemisphere controls and senses the opposite side of the body

Diencephalon

forms the walls of the third ventricle

parts of the diencephalon

thalamus, hypothalamus, pineal gland, pituitary gland, mammillary bodies

thalamus

• Relay center for motor and sensory information as it leaves or enters the brain

• The intermediate mass connects the two sides of the thalamus

hypothalamus

• Maintains homeostasis by coordinating the autonomic nervous system and pituitary gland

• It regulates body temperature, blood pressure, hunger, thirst, and sleep

pineal gland

• Located posterior to the thalamus

• senses the light/dark cycle and produces melatonin

pituitary gland

• Controls many other endocrine glands and regulates functions including development, growth, egg and sperm maturation, milk production, and thyroid activity

• It also releases adrenocorticotropic hormone, which signals the adrenal glands

mammillary bodies

• small, round structures on the underside of the hypothalamus

• part of the limbic system and are involved in memory formation and recollection

brainstem

the stalk-like lower part of the brain that connects the cerebrum and cerebellum to the spinal cord

parts of the brain stem

midbrain, pons, and medulla oblongata

midbrain

• Located above the pons

• Contains the cerebral aqueduct, corpora quadrigemina, and cerebral peduncles

corpora quadrigemina

Located on the posterior midbrain and includes the superior and inferior colliculi

superior colliculi

Associated with visual reflexes and help produce eye and head movements in response to sensory information

inferior colliculi

Auditory center; helps localize sound and recognize changes in pitch

cerebral peduncles/crus cerebri

Contain motor fibers traveling from the cerebrum toward the spinal cord

pons

• Located between the midbrain and medulla

• Contains mainly nerve tracts and cerebellar peduncles

• the peduncles connects the cerebellum to the brainstem

medulla oblongata

• located below the pons

• the medullary pyramids contains motor fibers on their way to the spinal cord

medullary pyramids

Contain motor fibers traveling toward the spinal cord

The fourth ventricle is located between the cerebellum and brainstem . . .

posterior to the brainstem/medulla

corpus callosum

• Band of transverse fibers that connects the left and right cerebral hemispheres and allows them to communicate

• It lies superior to the lateral ventricles

fornix

• White matter tract inferior to the lateral ventricles

• part of the limbic system

• associated with memory recall

cerebellum

• lies below the occipital lobe and behind the brainstem

• It is important for motor control, coordination, posture, and balance

lobes

anterior, posterior, and flocculonodular lobes

arbor vitae

The tree-like white matter inside the cerebellum that transmits signals between the cerebellum and other brain regions

cerebellar peduncles

Connect the cerebellum to the brainstem

damage to the cerebellum

Can cause ataxia (loss of coordination and balance) and may cause tremors

ventricles

spaces that contain/store cerebrospinal fluid (CSF)

lateral ventricles

One in each cerebral hemisphere, located in the lower medial portions of each hemisphere

septum pellucidum

Thin membrane that separates the lateral ventricles

choroid plexus

Capillaries interact with ependymal cells to secrete CSF

third ventricle

Located on the midline in the diencephalon

fourth ventricle

Located on the midline between the cerebellum and brainstem

cerebral aqueduct

Connects the third and fourth ventricles

the spinal cord

• the main communication pathway between the body and the brain

• It extends from the foramen magnum to approximately the L1–L2 vertebral level, where it ends as the conus medullaris

• There are 31 pairs of spinal nerves

cervical englargement

Supplies nerves for the upper limb. The slides give the region as C3–T1

lumbar enlargement

Supplies nerves for the lower limb. The slides give the region as L1–S2

conus medullaris

The tapered end of the spinal cord, at approximately L1–L2

cauda equina

Bundle of spinal nerve roots continuing below the end of the spinal cord

filum terminale

Anchors the spinal cord to the coccyx

gray matter in a spinal cord cross-section

• located centrally in a butterfly/H shape

• contains neuron cell bodies and is arranged into horns

white matter in a spinal cord cross-section

• Surrounds the gray matter

• contains mostly myelinated axons and ascending/descending tracts

dorsal (posterior) horn:

receives sensory input

ventral (anterior) horn:

Associated with motor output

lateral horn:

Contains sympathetic/ANS neuron cell bodies; the slides specify T1–L2

dorsal root:

Sensory signals enter the spinal cord through this root

dorsal root ganglion:

Contains sensory neuron cell bodies

ventral root:

Motor signals leave the spinal cord through this root