Nervous SystemsNervous Systems

Overview of a Nervous Overview of a Nervous SystemSystem

Overview of a Nervous SystemOverview of a Nervous System• Sensory Input

– conduction of signals from sensory receptors– PNS

• Integration– environmental information is interpreted– CNS (brain and spinal cord)

• Motor Output– conduction of signals to effector cells– PNS

NeuronsNeurons

NeuronsNeurons

• Cell body– nucleus and organelles

• Dendrites– short and branched– toward cell body

• Axons– long and unbranched– away from cell body

AxonsAxons

• Myelin Sheath - insulating layer

• Node of Ranvier - gaps between Schwann Cells

• Synaptic Terminals - neuron ending

Clusters of NeuronsClusters of Neurons

• Ganglion– Cluster of nerve cell bodies in the PNS

• Nuclei– Cluster of cells in the brain

Supporting CellsSupporting Cells

• Glia (glue)– Oligodendrocytes

• Form myelin sheath in brain

– Schwann Cells• Form myelin sheath in the PNS

ReflexReflex

• Sensory neuron to a motor neuron

Neural SignalsNeural Signals• Membrane Potential• Sodium-Potassium Pump

Threshold PotentialThreshold Potential

Resting StateResting State

• Both sodium and potassium activation gates are closed

• Interior of cell is negative

Depolarization StateDepolarization State

• Sodium activation gates are opened on some channels

• Interior of cell becomes more positive

Rising Phase of Action PotentialRising Phase of Action Potential

• Most sodium activation gates are opened

• Potassium activation gates are still closed

Falling Phase of Action PotentialFalling Phase of Action Potential

• Inactivation gates on sodium channels are closing

• Activation gates on potassium channels are opened

• interior of cell becomes more negative

UndershootUndershoot

• Both gates to sodium channels are closed

• Potassium channels are closing

• Membrane returns to its resting state

Propagation of Propagation of the Action the Action PotentialPotential

• Localized event• First action

potential’s depolarization sets off second action potential

• Travels in one direction due to refractory period

Salatory ConductionSalatory Conduction• Action Potential jumps from node to node• Speeds up signal from 5 m/sec to 150

m/sec

Communication Between Communication Between SynapsesSynapses

• Electrical Synapses– gap junctions allow for direct transfer of action

potential (used during escape responses)

• Chemical Synapses– uses neurotransmitters

Chemical SynapseChemical Synapse

Chemical SynapsesChemical Synapses• Action potential triggers an influx of calcium

• Synaptic vesicles fuse with presynaptic membrane

• Neurotransmitter released into synaptic cleft

• Neurotransmitters bind to receptors and open ion channels on postsynaptic membrane which sets off new action potential

• Neurotransmitters are degraded by enzymes or removed by a synaptic terminal

NeurotransmittersNeurotransmitters

Vertebrate Vertebrate Nervous Nervous SystemSystem

Central Nervous SystemCentral Nervous System

• Ventricles (4)– Cerebrospinal

fluid

• White Matter– Made up of

axons

• Gray Matter– Made up of

dendrites

Peripheral Nervous SystemPeripheral Nervous System

Peripheral Nervous SystemPeripheral Nervous System

• Autonomic Nervous System regulates the internal environment (usually involuntary)

• Somatic Nervous System regulates the external environment (usually voluntary)

Autonomic Nervous SystemAutonomic Nervous System

Autonomic Nervous SystemAutonomic Nervous System

• Sympathetic Division– Flight or fight response

• Parasympathetic Division– Rest or digest response

BrainBrain

The BrainstemThe Brainstem

• The Medulla Oblongata and the Pons controls breathing, heart rate, digestion

• The Cerebellum controls coordination of movement and balance

The MidbrainThe Midbrain

• The Midbrain receives, integrates, and projects sensory information to the forebrain

The DiencepholonThe Diencepholon

• Forebrain– Epithalamus

• Includes the pineal gland and the choroid plexus

– Thalamus• conducts information to specific areas

of cerebrum

– Hypothalamus• produces hormones and regulates body

temperature, hunger, thirst, sexual response, circadian rhythms

The TelencepholonThe Telencepholon

• Cerebrum– with cortex and

corpus callosum• higher thinking

CerebrumCerebrum

CerebrumCerebrum

CerebrumCerebrum

Limbic SystemLimbic System

• Regulates emotions– Association

with different situations is done mostly in the prefrontal lobe

MemoryMemory

• Short Term– Done in the

frontal lobe

• Long Term– Frontal lobes

interact with the hippocampus and the amygdala to consolidate

Sensory ReceptorsSensory Receptors

• Mechanoreceptors

• Pain Receptors

• Thermoreceptors

• Chemoreceptors

• Electromagnetic Receptors

Sensory ReceptorsSensory Receptors

• Mechanoreceptors• Pain Receptors• Thermoreceptors

Sensory ReceptorsSensory Receptors

• Chemoreceptors

Sensory ReceptorsSensory Receptors

• Electromagnetic receptors

Evolution of the Evolution of the EyeEye

• Complex eyes have developed many times

Evolution of the Evolution of the EyeEye • All light-sensitive organs rely

on photoreceptor systems employing a family of proteins called opsins. Further, the genetic toolkit for positioning eyes is common to all animals: the PAX6 gene controls where the eye develops in organisms ranging from mice to humans to fruit flies

PhotoreceptorsPhotoreceptors • Eye cups (ocelli) - light detection

• Genetic basis that started as a light detector 600 mya

• During the Cambrian explosion around 540 mya two types of eyes arose

PhotoreceptorsPhotoreceptors

• Compound Eyes - made up of ommatidia that helps detect movement

PhotoreceptorsPhotoreceptors

• Camera Type Eyes – Evolved several times– Hagfish eye– Lamprey eye– Jawed vertebrate

eyes

Single Lens EyeSingle Lens Eye

• Sclera (white)• Cornea (clear)• Choroid (pigmented)• Iris (color of eye)• Retina (rods and cones)• Pupil• Fovea (focal point)• Blind spot

PhotoreceptorsPhotoreceptors Scars of Evolution

1. inside out retina that forces light to pass through the cell bodies and nerves before hitting the retina

2. blood vessels across the retina that cause shadows

3. nerve fibers that exit causing a blind spot

FocusingFocusing• Near vision

– ciliary muscle contracted

– lens becomes more spherical

• Distance vision– ciliary muscle

relaxed– lens becomes

flatter

Visual ProblemsVisual Problems

• Near-sightedness (myopia)– eyeball too long / focal point in front of fovea

• Far-sightedness (hyperopia)– eyeball too short / focal point behind fovea

• Astigmatism (blurred vision)– misshapen lens or cornea

Hearing and EquilibriumHearing and Equilibrium

Hearing OrganHearing Organ• Outer Ear

– pinna and the auditory canal– tympanic membrane

• Middle Ear– malleus, incus and stapes– oval window

• Inner Ear– cochlea with the Organ of Corti

• with a basilar membrane and hair cells

• Eustachian Tube

SoundSound• Volume

– amplitude of sound wave– vibrates fluid in ear and bend hair cells which

generates more action potentials

• Pitch– frequency of sound wave

EquilibriumEquilibrium

• Utricle and Saccule• Semicircular Canals

– used to detect body position and movement

ChemoreceptionChemoreception

• Taste Buds– sweet (tip), salty

(behind), sour (sides), bitter (back of tongue)

ChemoreceptionChemoreception

• Olfactory receptors cells– upper portion of nasal cavity

The Cost of LocomotionThe Cost of Locomotion

The Cost of LocomotionThe Cost of Locomotion

• Locomotion must overcome two forces:– gravity– friction

• Swimming is more efficient than running– runner must overcome gravity

• Larger animals travel more efficiently than smaller animals

• Flight is the most costly (per minute)

Cooperation of Muscles and Cooperation of Muscles and SkeletonsSkeletons

• Muscles always contract

• Muscles attached in antagonistic pairs

Skeletal MusclesSkeletal Muscles

• Muscles are made up of muscle fibers

• Fibers are made up of myofibrils

• Myofibrils are made up of myofilaments– thin filaments (actin)– thick filaments (myosin)

Sliding Filament Sliding Filament ModelModel

• Sacromeres (basic functioning unit)– Z lines (border of

sacromeres)– H zone (center of

sacromere)– I band (only thin filaments)– A band (length of thick

filaments)

Sliding Filament Sliding Filament ModelModel

• During contraction, thin and thick filaments slide past each other– I band and H zone

decreases in size

• Caused by myosin head creating cross bridge with actin fiber and then moves by using ATP