BSCI201 LAB PRACTICAL 3

Nervous System

• Function: Controls body, voluntary and involuntary control, initiates voluntary skeletal movements, moderates heart rate and breathing rate, processes sensory inputs, controls speech, etc

Monitors and Processes Sensory Information:

• receives information from BOTH environment and inside body

• Nervous system divisions:

  • Central Nervous System (CNS) → consists of brain and spinal cord

    • Spinal cord → receives information and processes lower level involuntary responses (reflexes)

    • Brain → more complex information, higher order processing (processing sound information, forming speech, response, etc)

  • Peripheral Nervous System (PNS) → consists of cranial and spinal nerves, ganglia, and sensory receptors

  • Types of Cells:

    • Neurons → conducting cells

      • send electrical and chemical signals that deal with communication

    • Neuroglia → supporting cells

      • support and protect neurons

Types of Neuroglial Cells

• Means nerve glue; also known as glial cells

• Functions: Brace, protect, and myelinate neurons

  • not capable of transmitting nerve impulses

• Myelinating Cells → significantly high lipid content, making them appear white

• CNS Supporting Cells:

  • Astrocytes → control chemical environment of CNS, create blood-brain barrier, have extensions that wrap around neurons and blood vessels, etc

  • Microglia → phagocytic cells, engulf and destroy pathogens and debris from dead cells, protects cells of brain and spinal cord, etc

  • Ependymal Cells → ciliated columnar cells that line cavities of CNS filled with cerebrospinal fluid, cilia are motile and can beat, moving fluid and circulating CSF through cavities, etc

  • Oligodendrocytes → wrap around neurons, speed electrical transmissions that pass through neurons, etc

    • extend multiple processes away from main cell body and each processes wrap around a neuronal process

    • one oligodendrocyte can myelinate multiple neuronal processes

• PNS Supporting Cells:

  • Schwann Cells → myelinating cells of PNS, myelinate neuronal processes to insulate them and speed up conduction of electrical signals, etc

    • entire schwann cell will flatten and wrap its entire body around a neuron

    • can only myelinate one neuron

  • Satellite Cells

    • wrap around neurons to control chemical environment the neuron is exposed to

    • multiple cells surround the cell body of the neuron

Neuron Anatomy

• Cell Body → composed of large, round nucleus surrounded by cytoplasm, which contains:

  • Nucleus → large and round

  • Nucleolus → ribosome assembly

  • Neurofibrils → intermediate filaments of cytoskeleton

    • built from neurofilament proteins

    • form network throughout cytoplasm that allows cells to maintain shape

  • Chromatophilic substance → specialized rough ER of neurons

    • facilitates protein production and processing

  • main biosynthetic center of cell, where transcription and translation occur

  • receives information from various dendrites and processes information

  • sends signals via axon

• Dendrites and Axons → processes that extend out from the cell body and transmit nerve impulses

  • Dendrites → receive signals and sends them towards the cell body

    • contains many dendrites

  • Axons → transmit action potentials to other cells

    • carry electrical signals (action potentials) away from cell body and towards axon terminal

    • one neuron has one axon, but there can be many branching axon terminals

    • axon hillock → place of origin of axon near cell body

    • axon terminals meet with other cells and neurons via synapses, where electrical signals are converted into chemical signals

    • myeline sheath gaps → gaps between myelinating cells on axon

Structural Classification of Neurons

• Based on how many processes extend from cell body

• Multipolar: neurons have many dendrites and one axon

• Bipolar: neurons have one axon and one dendrite

• Unipolar (pseuounipolar): neurons have one process that branches; no dendrites

  • singular process is short and divides into proximal and distal branches

    • distal peripheral process → associated with sensory receptor

    • proximal central process → enter CNS and synapse onto neuron of CNS

  • unipolar neurons are derived from bipolar neurons

Functional Classification of Neurons

• Based on the direction of impulse transmission in relation to CNS

• Sensory (afferent) neurons → carry impulses from sensory receptors in skin, internal organs, muscles, and special sense organs TOWARDS CNS

• Association neurons (interneurons) → conduct impulses within CNS

• Motor (efferent) neurons: carry impulses AWAY from CNS to organs, muscles, and glands

Neuron Properties

Tracts and Nerves

• Tract: bundle of axons in CNS supported only by neuroglia

• Nerve: bundle of axons in PNS wrapped in CT

  • Sensory (afferent) nerves: contains only sensory processes

  • Motor (efferent) nerves: contain only motor processes

  • Mixed nerves: contain both sensory and motor neurons

• Connective Tissue Sheathes of Nerves:

  • Endoneurium → encloses each axon and its myelin sheath

  • Perineurium → encloses groups of axons called fascicles

  • Epineurium → encloses nerve (group of fascicles)

Human Brain Gross Anatomy

• Weight: 3.5 lbs (1.6 kg)

• Four Major Regions:

  • Cerebrum

  • Diencephalon

  • Brain Stem

  • Cerebellum

Anatomy of Cerebrum

• composed of two cerebral hemispheres (left and right)

• 83% of brain’s total mass

• surface of cerebrum is marked by gyri (elevated ridges)

  • sulcus → furrow between gyri

  • fissure → deeper sulcus

• each cerebral hemisphere is divided into five lobes

Cerebral Hemispheres

• carries out higher mental functions (memory and reason)

• separated by longitudinal fissure → median fissure dividing cerebrum into right and left hemispheres

• held together medially by corpus callosum

• lateral ventricles separated by membrane (septum pellucidum)

Cerebrum 5 Lobes

• frontal, temporal, parietal, and occipital lobes:

  • can be viewed externally

  • named for the overlaying cranial bones

• Insula

  • cannot be viewed externally

  • located deep to the lateral sulcus (covered by frontal, temporal, and parietal lobes)

Cerebrum Major Sulci

• central sulcus → separates frontal and parietal lobes

  • precentral gyrus of frontal lobe contains primary motor cortex

  • postcentral gyrus of parietal lobe contains primary somatosensory cortex

• lateral sulcus → separates temporal lobe from parietal and frontal lobes

• parieto-occipital sulcus → separates parietal lobe from occipital lobe

Three Major Regions in Cerebral Hemispheres

• cerebral cortex → composed of grey matter (cell bodies and dendrites)

  • highly convoluted

  • 2-4 mm thick

  • 40% of total brain mass

  • location of conscious mind

• white matter → tracts with myelinated axons (appear white)

  • deep to cerebral cortex

• basal nuclei → islands of cell bodies within cerebral white matter

Anatomy of Other Brain Regions

• Diencephalon → originates from forebrain, along with cerebrum

  • contains thalamus, epithalamus, and hypothalamus

• Brain stem → contains structures of midbrain, pons, and medulla oblongata

• Cerebellum → composed of two hemispheres connected by the vermis

  • contains thin superficial layer of gray matter and deep layer of white matter (arbor vitae)

  • coordinates skeletal muscle movements

Diencephalon

• Thalamus → relay center for all sensory information (except smell) on its way to cerebral cortex

• Hypothalamus → regulation of visceral activities and body functions, emotions, instincts, secretes hormones

• Epithalamus → contains pineal gland, which secretes the hormone melanin

Brain Stem

• Midbrain

  • corpora quadrigemina → pair of superior colliculi (visual reflex) and pair of inferior colliculi (auditory reflex)

  • cerebral peduncles → tracts in midbrain, connects pons to cerebrum

  • cerebral aqueduct → pathway for CSF

• Pons → contains fiber tracts connecting cerebrum to cerebellum

• Medulla oblongata → regulates autonomic functions (heart rate, blood pressure, breathing, etc) and it blends in with the spinal cord at the level of the foramen magnum

Cerebellum

• two hemispheres separated by a longitudinal fissure called the vermis

• thin superficial layer of gray matter and deep layer of white matter (arbor vitae)

• coordinates skeletal muscle contractions

  • specializes fine movements

  • helps lean new movements (walking)

  • brain region most affected by alcohol intoxication

Structures Protecting Brain

• cranium → body helmet composed of 8 cranial bones

• Meninges → three CT membranes surrounding the brain

• CSF → fluid cushion in the subarachnoid space and ventricles

• Blood-brain barrier → selective barrier that prevents harmful substances in blood from crossing into the brain

Meninges Anatomy

Cerebrospinal Fluid

• acts as fluid cushion, providing buoyancy

• provides nutrients and removes metabolic wastes

• filtered from blood by the choroid plexuses (small collections of capillaries in ventricles)

  • supported by astrocytes

• circulating through ventricles and in subarachnoid space → CSF found inside and outside brain

  • circulation facilitated by ciliated ependymal cells

12 Pairs Cranial Nerves

Cranial Nerve Modality + Function

Accessory Structures of Eye

• palpebrae → eyelids

• medial and lateral commissures

• lacrimal caruncle → fleshy elevation at medial commissure

• lacrimal apparatus → produces and drains tears to lubricate eye

Lacrimal Apparatus

• produces and drains lacrimal fluid (tears) to lubricate the eye

  • contains mucus, antibodies, lysozyme

• lacrimal fluid is continuously released and flows across the eye:

  • lacrimal gland

  • lacrimal puncta

  • lacrimal canaliculi

  • lacrimal sac

  • nasolacrimal duct

Extrinsic Muscles of Eye

Eye Wall Layers

• Fibrous Layer → composed of sclera and cornea

• Vascular layer → contains choroid, ciliary body, and iris

• Sensory layer → retina, composed of the pigmented and neural layers

Fibrous Layer (Outermost Eye Wall Layer)

• composed of dense avascular connective tissue

• sclera → opaque region occupying the posterior 5/6 of the fibrous layer

• cornea → anterior transparent region, modified to let light in

  • major light-bending medium of eye (refracts light to focus on the retina)

Vascular Layer (Middle Eye Wall Layer)

• choroid → highly vascularized posterior region, contains melanin to prevent the scattering of light

• ciliary body → encircles lens

  • ciliary muscle → intrinsic muscle that controls lens shape

  • ciliary processes → contain capillaries from which aqueous humor is filtered

  • zonules → fibers extended from ciliary process to hold the lens upright

• Iris → pigmented smooth muscles that regulate diameter of pupil

  • sphincter pupillae → contract to constrict the pupil (close vision and bright light)

  • dilator pupillae → contracts to dilate the pupil (distant vision and dim light)

Retina (Innermost Eye Wall Layer)

• pigmented layer (outer layer) → composed of melanocytes, absorbs light and prevents it from scattering

• neural layer (transparent inner layer) → converts light energy into nerve impulses that then travel to brain via optic nerve

  • fovea centralis → area of neural layer that contains only cones

  • optic disc (blind spot) → region where optic nerve fibers exit the eye, lacks photoreceptors

Cells of Neural Layer of Retina

• Two types of photoreceptors sense light:

  • rods → dim light vision

  • cones → high light and color vision

• Bipolar cells

• Ganglion cells → axons leave the retina in the optic nerve

Anterior vs Posterior Eye Segments

• anterior segment → between cornea and lens (includes lens)

  • contains aqueous humor, fluid formed and drained throughout life

  • lens → biconvex structure that helps focus light on retina

• posterior segment → everything posterior to lens

  • contains vitreous humor, a gel-like fluid formed during embryonic development that lasts a lifetime

• like lens, aqueous humor and vitreous humor help refract light

External Ear

• Pinna → elastic cartilage covered with skin

• external acoustic meatus → canal in temporal bone, lined with ceruminous glands

• tympanic membrane → vibrates in response to soundwaves; separates external and middle ear

Middle Ear

• three ossicles transmit and amplify vibrations

  • malleus → attached to tympanic membrane and incus

  • incus → articulates with malleus and stapes

  • stapes → articulates with incus and attaches to oval window

• oval window → transmits vibrations from stapes to Scala vestibuli

• pharyngotympanic tube → connects middle ear to throat

Internal Ear

• bony labyrinth → cavity in temporal bone, filled with perilymph

  • semicircular canals

  • vestibule

  • cochlea

• membranous labyrinth → ducts and sacs within body labyrinth, filled with endolymph

  • Equilibrium:

    • semicircular ducts

    • saccule

    • utricle

  • Hearing

    • cochlear duct

Spiral Organ - Responsible for Hearing

• Spiral organ (organ of corti) is within cochlear duct

• hair cells (auditory receptors) rest on basilar membrane and project stereocilia into tectorial membrane

• movement of basilar membrane bends the stereocilia, depolarizing hair cell membrane, starting nerve impulse in the cochlear nerve

Crista Ampullaris

Olfaction and Gustation

• chemical senses

• olfaction: sense of smell

• gustation: sense of taste

• receptors for olfaction and gustation are called chemoreceptors:

  • chemoreceptors respond to chemicals dissolved in aqueous solution

  • gustation chemoreceptors are divided into 5 subtypes that sense diff tastes

  • olfaction chemoreceptors are sensitive to wide range of chemical sensations

Olfaction + Olfactory Epithelium

• cell types of olfactory epithelium:

  • olfactory sensory neurons → bipolar neurons with radiating olfactory cilia

    • bundles of axons of olfactory receptor cells form the filaments of olfactory nerve

    • replaced every 30-60 days by olfactory stem cells

  • supporting cells → surround and cushion the olfactory system neurons

  • olfactory stem cells → lie at the basal surface (superior side of epithelium) and divide to replace olfactory sensory neurons

Sense of Taste

• receptor organs are taste buds

  • most located on tongue in papillae

  • few found on soft palate, epiglottis, pharynx, and inner surface of cheeks

• types of papillae:

  • fungiform → most numerous papillae, taste buds are on superior surface

  • foliate → on lateral edges of tongue, taste buds located in the side walls

  • vallate → large papillae in a V formation on posterior surface of tongue, taste buds are located in the side walls

Taste Bud Structure + Chemicals

• flask-shaped

• all taste buds response to all 5 classes of chemical stimuli

  • each taste bud responds optimally to one type of taste

• contain 50-100 epithelial cells

  • gustatory epithelial cells → receptor cells

    • microvilli (gustatory hairs) project through a taste pore to the surface of the epithelium bathed in saliva

  • basal epithelial cells → stem cells that replace the gustatory epithelial cells every 7 days

Endocrine System

• endocrine glands → ductless glands that release chemical regulators called hormones directly into ECF (interstitial fluid and blood)

• Endocrinology → study of biological effects of hormones released by endocrine glands and diseases caused by dysfunction

Major Endocrine Glands

Hormone Release

• released in response to homeostatic imbalances referred to as stimuli

• hormones usually work via negative feedback to maintain homeostasis

  • biological effects of hormones negate/eliminate stimuli that caused release of hormones

  • exception: hormone prolactin stimulates milk production through positive feedback

Stimuli Types

• Humoral stimuli → changes in levels of chemicals in body’s humors (bodily fluids) stimulate endocrine glands to release hormones

• Neural stimuli → activation of nervous system stimulates endocrine glands to release hormones

• hormonal stimuli → released hormones stimulate endocrine glands to release other hormones

Hormone Nomenclature

• organ of origin → endocrine gland releasing hormone

  • example: parathyroid hormone

• function → major biological effect of hormone

  • example: follicle stimulating hormone

• chemical structure → unique feature of chemical structure

  • example: triiodothyronine (t3)

Chemical Structure of Hormones Classes

• biogenic amine hormones → derived from amino acid tyrosine

• peptide/protein/glycoprotein hormones → composed of amino acid sequences

• steroid hormones → derived from cholesterol

Target Cells/Tissues of Hormones

• express accessible, functional receptors that hormones bind to

• multiple hormones can target same cell

• target cell can bind multiple hormones simultaneously

Pituitary Gland (Hypophysis)

• two functional lobes attached to the hypothalamus by infundibulum:

  • adenohypophysis (anterior)

    • controlled by neurosecretions produced by neurons of ventral hypothalamus then liberated into hypophyseal portal system and carried to cells of adenohypophysis where they control hormone release

      • produces 4 tropic hormones that stimulate target organs that are endocrine glands

      • produces 2 other main hormones not directly involved in regulation of other endocrine glands

  • neurohypophysis (posterior)

Pituitary Gland (Hypophysis)

• Neurohypophysis: not an endocrine gland but storage for 2 hormones transported to it via the axons of neurons in the paraventricular and supraoptic nuclei of the hypothalamus

Thyroid Gland

• located in throat just inferior to larynx

• two lobes joined by central mass or isthmus

Parathyroid Glands

• embedded in posterior surface of thyroid gland

Adrenal Glands

Pancreas

• located behind stomach

• functions as endocrine and exocrine gland

  • exocrine: produces digestive enzymes

  • endocrine: produces insulin and glucagon, hormones that act to regulate blood sugar levels

Gonads

• two tropic hormones released by anterior pituitary induce the gonads to produce steroidal hormones

  • follicle stimulating hormone (FSH)

  • luteinizing hormone (LH)

• Ovaries (females) produce estrogens and progesterone

• Testes (males) produce testosterone

Endocrine Disorders