Neuroscience weeks 1-5

Nervous system divided into

CNS and PNS

Central nervous system components

Brain

Spinal cord

Peripheral nervous system

• consists of sensory and motor fibres to and from CNS

• 12 pairs of cranial nerves - emerge from base of brain

• 31 pairs of spinal nerves - emerge between vertebrae

PNS divisions

Somatic nervous system

Autonomic nervous system

Somatic nervous system

• innervates skeletal musculature

• controls voluntary actions

Autonomic nervous system

= visceromotor system

• innervates internal organs and other visceral structures

• controls automatic actions

Autonomic nervous system divisions

• Sympathetic system

• Parasympathetic system

Sympathetic nervous system

• in sympathy with emotions

• fight or flight response

• e.g. dilated pupils, dry mouth, fast heart rate

Parasympathetic system

• Restoration of body’s energy

• digest

• causing pupils to constrict

Neurons

= nerve cells

• basic structural and functional unit of NS

• use electrochemical impulses

• receive, integrate and transmit info

Neuron communicates with postsynaptic cell

• Other neuron - via synapse

• smooth muscle fibre or grand - via neuroeffector junction

• skeletal muscle fibres - via neuromuscular junction

Functions of neurons

• Afferent

• Efferent

• Association

Afferent neurons

• bring impulses toward the CNS

• adding to CNS

Efferent neurons

• Carry impulses away from CNS to periphery

• exiting CNS

Association neurons

Interconnections in brain and spinal cord

e.g. interneuron

Neuroglia

= glia cells

Support cells of NS

Types of neuroglia

• Astrocytes

• Oligodendrocytes (CNS) and Schwann cells (PNS)

• Microglia

Astrocytes

• main type of glia, most numerous

• structural support, metabolic fxns and regulate passage of molecules between bloodstream and CNS

Oligodendrocytes (CNS) and Schwann cells (PNS)

Wrap axons in myelin sheath to increase speed of conduction/transmission of electrochemical signal

Microglia

Help to regulate brain development, maintenance of neuronal networks, injury repair and waste clearance

Grey matter

mainly cell bodies, dendrites and synapses

White matter

nerve fibres with lipid-rich myelin sheaths - myelinated axons

Nucleus

collection of neuronal cell bodies in CNS

Tract

Bundle of axons with common point of origin and termination, in CNS

Fasciculus

2 or more tracts running in company, in CNS

Ganglion

Collection of neuronal cell bodies, in PNS

Nerve

Bundle of axons in PNS

What are the two main parts of the human nervous system?

Central nervous system (CNS) and Peripheral nervous system (PNS).

Brain broken up into 3 sections

Cerebrum

Brainstem

Cerebellum

Cerebrum hemispheres

• 2, L and R

• separated by longitudinal fissure

• connected by corpus callosum

• some functions of hemispheres lateralised, e.g. left hemisphere dominant for language in most people

What separates the cerebrum from the cerebellum?

The transverse fissure

Cerebrum - grey matter

Cerebral cortex - 2-4mm grey matter, gyri and sulci (convolutions - maximize SA)

What separates the frontal lobe from the parietal lobe?

Central sulcus.

What separates temporal lobe from rest of brain?

Sylvian (lateral) fissure

What separates the parietal and occipital lobes?

Parieto-occipital sulcus

Frontal lobe

• largest lobe

• houses Broca’s area

• prefrontal cortex houses primary motor area

Primary motor area

• region of the frontal lobe responsible for voluntary movement controls

• located on precentral sulcus

Primary somatosensory area

• located in parietal lobe

• responsible for processing sensory information from the body, such as touch, temperature, and pain.

Angular and supramarginal gyrus

• located in parietal lobe

• important for connections from Broca’s to Wernicke’s area

Temporal lobe houses

• Wernicke’s area - important for language comprehension: spoken, written and gestures

• primary auditory area

Primary auditory area

Responsible for initial detection and processing of auditory info, where first auditory info gets passed to

Occipital lobe

• smallest lobe

• houses primary visual area

Grey matter structures within cerebrum

Basal ganglia - striatum (corpus striatum)

Caudate nucleus

Lentiform nucleus - putamen, globus pallidus

Amygdala

Diencephalon - thalamus, hypothalamus

Types of white matter fibres in the cerebrum

• association

• projection

• commissural

Association fibres

• small u-shaped = short distance connections

• fascicles = long distance connections within hemisphere

Projection fibres

• afferent = carry sensory info from body to brain

• efferent = carry motor impulses from brain & spinal cord

• most travel through corona radiata

• axons from corona radiate gathered into internal capsule

What type of fibers connect corresponding cortical areas in both hemispheres?

Commissural fibers.

e.g. corpus callosum

Brain stem divisions

• midbrain

• pons

• medulla oblongata

• Base - mainly descending axons

• Tegmentum - nuclei of CN 3-12, reticular formation (brain stem reflexes e.g. cough, gag), ascending sensory tracts

What are the three layers of protective membranes covering the CNS?

Dura mater, Arachnoid mater, and Pia mater.

Cerebellum

• 2 cerebellar hemispheres, vermis connects them

• outside = grey matter

• inside = white matter

• connected to brainstem by cerebellar peduncles

What part of the brain controls posture, muscle tone, and coordination?

Cerebellum.

Spinal cord

• continuation of brainstem

• protected by vertebral column

What is the function of the spinal cord?

Transmission link between brain and body

• motor info: brain to muscles, visceral organs, glands

• somatosensory info: from periphery to brain

• pain touch, temp

• controls many body reflexes

Spinal cord structure

• H-shaped core of grey matter

• Outside = white matter

• Ventral horn with ventral roots - motor axons to periphery

• dorsal horn with dorsal roots - sensory axons bringing info to spinal cord

What is decussation in the context of the cerebrum?

The crossing of sensory and motor fibers at some point, resulting in contralateral processing.

Protective coverings of CNS

• skull and vertebral column

• cranial and spinal meninges

Cranial & spinal meninges

3 layers of protective membranes:

• dura mater - tough, attached to inside of skull

• arachnoid mater - resembles cobweb, doesn’t follow gyri and sulci

• pia mater - delicate, follows surface of brain

What space lies between the arachnoid mater and pia mater?

Subarachnoid space, filled with cerebrospinal fluid.

Sutures

Joints of the cranial bones, where different parts of the skull connect, appear as jagged lines

• coronal

• sagittal

• lamdoidal

• occipitomastoid

Foramen

Hollow passage way, opening

Skull landmarks

• orbits

• nasal septum

• nasal conchae

• frons - forehead

• occiput - posterior (back of head)

• vertex - superior (highest point)

• Temporae - temple

Skull landmarks continued

• calvaria - skullcap

• cranial fossa - anterior, medial, posterior

• foramen magnum - spinal cord, vertebral arteries, spinal arteries

• external auditory meatus - ear canal

• mastoid process

• styloid process

• sutures: coronal, sagittal, lamdoidal, occipitomastoid

Cranial bones

8 in total:

• frontal

• temporal x2

• parietal x2

• occipital

• ethmoid

• sphenoid

protects the brain

attachment for membranes and muscles

Frontal bone landmarks

• supraorbital margin

• squamous portion

• zygomatic process

Temporal bones landmarks

• zygomatic process

• mastoid process

• mandibular fossa

• styloid process

• external auditory/acoustic meatus

• internal auditory/acoustic meatus

Parietal bones

• forms the sides and roof of the cranium/skull

• sagittal suture

Occipital bone landmarks

• foramen magnum - hole that allows brain stem and vessels through

• occipital condyles - rounded areas which allow connection to the vertebrae, allow head to move in different ways, forms joint with vertebrae

Sphenoid bone

forms bottom bits of orbits

Ethmoid bone

• rests on top of sphenoid bone

• perpendicular plate which helps form nasal septum

Facial bones

14 in total, majority have left and right

• maxillae x2

• mandible

• zygomatic x2

• nasal x2

• palatine x2

• lacrimal x2

• vomer

• inferior nasal concha x2

Maxillae landmarks

upper jaw - forms anterior 2/3 of hard palate

• zygomatic process

• frontal process

• alveolar process - houses upper teeth

• intermaxillary suture- where the L & R sections meet

• palatine process

• incisive foramen

Palatine bones

• form posterior 1/3 of hard palate

Mandible landmarks

lower jaw bone

• body

• angle

• ramus - coronoid process, condylar process, mandibular notch

Mandible landmarks cont.

• mental symphysis

• mental protuberance

• mental tubercles

• alveolar ridge - dental alveoli

Mandible - mylohyoid line

• important for speech and swallowing

• connects all the way inside the mandible

Zygomatic bones

• cheekbones

• helps form orbits and cheeks, allow for attachment of muscles

Nasal bones

• form bridge of nose

Inferior nasal concha

Lacrimal bones

• help form orbits

Vomer

• helps form nasal septum

• exists in midline

Arteries

carry oxygenated blood to brain or tissue

Veins

return deoxygenated blood back to heart

Capillaries

• very small blood vessels between arteries and veins that distribute oxygen-rich blood to the body

• join arterial system to venous system, allowing exchange of oxygen and nutrients

Vascular network - aorta

• main artery

• carries blood from left ventricle to all parts of body (except lungs)

Aortic arch divides into 4 branches

• 2 carotid arteries: internal and external carotid

• 2 subclavian arteries: left and right vertebral arteries

What two arterial systems supply blood to the brain?

• Internal carotid arteries (anterior - towards the front)

• vertebral arteries (posterior - towards the back)

Internal carotid arteries

• Middle Cerebral Artery (MCA)

• Anterior Cerebral Artery (ACA)

Middle Cerebral Artery (MCA)

• supplies lateral surface of frontal, parietal & temporal lobes

• comes up sylvian fissure

• supplies 80% of carotid blood

• major areas for: motor and sensory functions, speech

Anterior Cerebral Artery (ACA)

• supplies medial surface of frontal & parietal lobes, corpus callosum, basal ganglia

• much smaller than MCA

• supplies 20% of carotid blood

Vertebral arteries

• give off numerous branches that supply: spinal cord, medulla, pons, midbrain & cerebellum

• at lower border of pons: merge to form 1 basilar artery (in front of brain stem), then divide into 2 posterior cerebral arteries (PCA)

Posterior cerebral arteries (PCA)

• supplies lateral & inferior temporal lobes

• supplies lateral & medial occipital lobes

Watershed areas

Vascular border zones

• where small-end branches of cerebral arteries approach each other

Circle of Willis (CoW)

• at base of brain, arteries linked by communicating vessels

• connects posterior supply of brain to anterior supply

• Provides some redundancy, if blockage in one vessel another vessel can supply blood, allows blood to move from right side to left side and front and back of brain

Brainstem’s blood supply

Cerebellar & Spinal Cord blood supply

Vascular network

Function of blood

• supplies nutrition: glucose and oxygen

• remvoes metabolic waste

Why do neurons need an uninterrupted supply of oxygenated blood to function?

• can’t store glucose and oxygen sources

Cerebrovascular accident (CVA)

• stroke

• brain damage caused by sudden vascular disruptions

• 2 main types: ischemia and hemorrhage

Ischemia

• blocked artery resulting in part of brain losing blood supply

• most common type of CVA’s, > 80%

• 2 types: thrombosis and embolism