1. Neurobiology 3 and 4

W2 Southard

What are the three layers of the meninges?

1. Dura

2. Arachnoid

3. Pia

What are the three spaces of the meninges?

1. Epidural

2. Subdural

3. Subarachnoid

What are the characteristics of the dura mater (pachymeninges)?

- tough and fibrous

- outer layer

- 2 key infoldings separate parts of the brain

- encompasses venous sinuses

- function = protection

What are the two infoldings of the dura mater?

- Faux cerebri (between the cerebral hemispheres right and left)

- Tentorium cerebelli (between cerebrum and cerebellum)

What are the characteristics of the arachnoid mater (Leptomeninges)?

- spider web appearance

- forms granulations that reabsorb CSF

- location of small arteries

- function = cushioning and absorption of CSF

What are the characteristics of the pia mater (leptomeninges)?

- delicate membrane

- follows the gyri and sulci of the brain

- function = barrier, blood vessel penetration

What do the meninges look like all put together?

What is the epidural space?

between bone and dura

What is the subdural space?

potential space between arachnoid and dura mater

What is the subarachnoid space?

space between arachnoid and pia mater- contains CSF

What vessels provide blood flow to the brain? (general)

• Brain Arterial Supply: The brain receives 15–20% of cardiac output despite comprising only ~2% of body weight.

  • Blood is supplied by two sets of paired arteries:

    • Internal Carotid Arteries

    • Vertebral Arteries

      • oin along the ventral surface of the medulla to form the basilar artery.

What is the Circle of Willis?

a ring of arteries at the base of the brain that connects the brain's anterior and posterior circulations

What parts of the brain does the circle of Willis supply?

What are the parts of the venous drainage of the brain?

https://skfb.ly/orwWW

What is the dorsal spinal artery?

it supplies the dorsal white matter and grey matter

What is the ventral spinal artery?

supplies the ventral and lateral white and grey matter

What are the two major veins of the spinal cord?

1. dorsal spinal vein

2. ventral spinal vein

What is the function of the blood brain barrier?

protect the neural tissue from pathogens and toxins in the bloodstream.

What are the components of the blood brain barrier?

1. endothelial cells with tight junctions

2. basement membrane

3. pericytes- contractile cells

4. astrocyte foot processes

How was the blood brain barrier discovered?

intravenous injections of dyes into mice stained all tissues except the brain (no dye in the CSF)

The choroid plexus and meninges were stained

• NOT the brain itself!

What is cerebrospinal fluid?

- clear, colorless fluid

- fills the ventricular system and subarachnoid space

- Produced by choroid plexus from blood

• produced from plasma but very different in quality and content

What are the functions of cerebrospinal fluid?

1. protection/ shock absorption

2. homeostasis

3. clearance of waste products

What is the choroid plexus?

• specialized ependymal cells that form papillary structures containing many blood vessels

  • located in lateral, third, and fourth ventricles

• use a variety of pumps and channels to form CSF from the blood

Where is cerebrospinal fluid produced?

in the lateral, third, and fourth ventricles

Describe the flow of CSF?

1. lateral ventricles

2. interventricular foramen

3. third ventricle

4. mesencephalic aqueduct

5. fourth ventricle

6. medial and lateral foramens

7. subarachnoid space

Spinal tap???

• either in cranial or lat. dorsal

• SITES

  • Cerebellomedullary cistern (cisternal tap)

  • Lumbar cistern (lumbar tap)

• Risks:

brain herniation (sudden pressure shift forces nervous tissue out)
• Safe volume: ~0.5 mL/kg per day
• Sterile technique should always be used

What are spinal nerves?

they arise from the spinal cord

What structures do the spinal nerves innervate?

structures caudal to the head

where are the cell bodies of the spinal nerves located?

in the dorsal root ganglia (sensory) or ventral horn (motor)

True/false- spinal nerves are mixed (sensory and motor)

TRUE

How are the spinal nerves numbered?

by the corresponding spinal cord segment (the # varies by species)

They may also combine to form plexuses and named nerves (the sciatic nerve is formed from spinal nerves L6, L7, and S1)

What are cranial nerves?

they arise from the brain

What structures do cranial nerves innervate?

structures in the head and neck

True/false- cranial nerves are mixed (sensory and motor)

FALSE- they can be sensory, motor, or mixed (sensory and motor)

Where are the cell bodies of cranial nerves located?

in the nuclei within the brain or ganglia outside the brain

How many cranial nerves are there?

12 pairs (designated I-XII)

The dorsal and ventral roots connect with the _________________

spinal cord

The spinal nerve splits into ______________________

dorsal and ventral branch/ramus

The dorsal branch is sensory/motor to the _________________

back

The ventral branch is sensory/motor to the ______________________________

ventral body wall, limbs, and visceral organs

each sensory spinal nerve innervates a strip of skin called a __________________________

dermatome:

• an area of skin in which sensory nerves derive from a single spinal nerve root

it also detects sensations in muscle, organs, and connective tissue

where are the cell bodies for sensory neurons located?

in the dorsal root ganglia

where are the cell bodies for motor spinal nerves located?

in the ventral horn

Spinal motor nerve branches combine to innervate specific ______________

muscles

What is the structure of the peripheral nerves?

1. the axons can be myelinated or unmyelinated

2. connective tissue (endoneurium, perineurium, epineurium)

3. Schwann cells (myelinate axons)

4. blood vessels

What is the endoneurium?

wraps around individual axons

What is the perineurium?

wraps around bundles of axons

What is the epineurium?

wraps around nerves

What are the characteristics of peripheral nerves?

1. white

2. solid and do not stretch (differentiate nerves from arteries)

3. typically run in the fascia between muscle bodies

4. may parallel the blood vessels (neurovascular bundle)

What are the divisions of the peripheral nervous system?

What is the function of the autonomic nervous system?

regulates involuntary physiologic processes (heart rate, blood pressure, respiration, digestion, sexual functioning)

The autonomic nervous system is composed of the _________________________

sympathetic, parasympathetic, and enteric systems

What is the function of the somatic nervous system?

conscious sensation and voluntary movement

What are the effector organs of the autonomic nervous system?

smooth muscle, glands, and cardiac muscle

What are the effector organs of the somatic nervous system?

skeletal muscle

What are the motor pathways of the autonomic nervous system?

two neurons that synapse outside of the CNS

What is the motor pathway of the somatic nervous system?

One neuron, cell body in CNS

What are the differences between the sympathetic and parasympathetic nervous systems?

Cholinergic receptors bind _________________

Ach/ acetylcholine

• nicotinic and muscarinic receptors

What is the difference between preganglionic and postganglionic neurons?

Preganglionic:

• The cell bodies of the preganglionic neurons are in the brainstem or spinal cord of the central nervous system (CNS).

Postganglionic:

• The cell bodies of the postganglionic neurons are in autonomic ganglia located peripherally.

Axon terminal of preganglionic neurons synapse on dendrites and cell bodies of postganglionic neurons.

What are muscarinic receptors?

They are postganglionic parasympathetic

activated by the molecule acetylcholine

What are nicotinic receptors?

Preganglionic and somatic

activated by acetylcholine

Adrenergic (alpha, beta) receptors bind to ______________________

norepinephrine

What are alpha and beta receptors?

postganglionic sympathetic

What are the functions of the sympathetic nervous system?

1. fight, flight, fright response

2. activated in times or stress

3. increased heart rate and respiratory rate

4. increased blood flow to muscles

5. decreased digestive processes

6. innervates nearly every tissue in the body

7. ganglia located in a chain adjacent to the spinal cord

The motor pathways of the sympathetic nervous system involves ____________ neurons

TWO

What what are the characteristics of the preganglionic neuron in the motor pathways of the SNS?

- short axon

- cell bodies in intermediolateral cell column

- synapses in sympathetic ganglion

- neurotransmitter = Ach, receptor = nicotinic

What are the characteristics of the postganglionic neuron in the motor pathways of the SNS?

- long axon

- cell bodies in sympathetic ganglion

- synapses on effector organ

- NT = norepinephrine, receptor = alpha or beta

The sensory pathways of the sympathetic nervous system is ________________

similar to somatic nervous system

cell bodies in dorsal root ganglion

Where are the adrenal glands located?

located cranial and medial to kidney

What does the endocrine gland do?

releases chemical messengers into the blood

what are the parts of the adrenal gland?

1. cortex = controlled by the pituitary gland

2. medulla = controlled by sympathetic nerves (releases catecholamines (epinephrine and norepinephrine)

What are the functions of the parasympathetic nervous system?

1. rest and digest

2. decreased heart and respiratory rate

3. increased digestion

4. ganglia and located in or near the target organ

Parasympathetic ganglion are located ____________________________

in or near target organ

What are the characteristics of the preganglionic neuron in the motor pathway of the PSNS?

- long

- cell bodies in brain and cervical spinal cord

- synapses in ganglia near or in target organ

- neurotransmitter = Ach

- receptor = nicotinic

What are the characteristics of the postganglionic neuron in the motor pathway in the PSNS?

- short

- cell bodies in parasympathetic ganglia

- synapses on effector organ

- neurotransmitter = Ach

- receptor = muscarinic

The sensory pathways of the PSNS is similar to ____________________

cranial and spinal nerves

How does the sympathetic and parasympathetic nervous systems differ in how they regulate functioning organs?

What is the enteric nervous system?

a web-like series of neurons located in the wall of the intestine

Circle of Willis

Formed by the basilar artery and internal carotid arteries. Major branches include:

• Caudal Cerebellar Arteries: Arise directly off the basilar artery.

• Circle of Willis Branches: Rostral cerebellar, caudal cerebral, middle cerebral, and rostral cerebral arteries.

Regional Distribution of arteries to the Telencephalon

Supplied by the rostral, middle, and caudal cerebral arteries.

Regional distribution of arteries to the diencephalon + mesencephalon

Supplied by perforating arteries.

Regional distribution of arteries to the rhombencephalon

Supplied by the vertebral, caudal, and rostral cerebral arteries.

Venous drainage of the brain

Small veins drain into venous sinuses located between folds of dura mater.

• These sinuses drain into the internal jugular veins, which return blood to the heart via the cranial vena cava.

Spinal cord blood supply and drainage

• Delivered by a midline ventral spinal artery and paired dorsal spinal arteries located within the dura mater (arising from aortic branches).

• Drained by ventral and dorsal spinal veins.