NEUROMUSCULOSKELETAL SYSTEMS
LECTURE 2
EXCITABLE CELLS
Medical Science
Dr R G Luckwill
Input Zone
Dendrites
and
Cell body
Nucleus
Trigger Zone
Axon hillock
Conducting Zone
Axon (may be from 1mm
to more than 1m long)
Arrows indicate the
direction in which nerve
signals are conveyed.
Output Zone
Axon terminals
Figure 4.10
Page 94
Secretory
vesicle
Kinesin
molecule
Microtubule
Endoplasmic
reticulum
Nucleus
Golgi
complex
Secretory
vesicle
Microtubular “highway”
Axon
Lysosome
Debris
Axon
terminal
Cell body
Figure 2.18
Page 43
Penetration
Diffusion down Concentration Gradient
= Solute molecule
Net diffusion
(diffusion from area A
to area B minus diffusion
from area B to area A)
Figure 3.7 (1)
Page 61
Electrical Gradient
Negatively
charged area
Positively
charged area
Cations (positively charged ions)
attracted toward negative area
Anions (negatively charged ions)
attracted toward positive area
Page 63
If a substance can
permeate the membrane:
If the membrane is
impermeable to a substance:
Figure 3.8
Page 62
Exocytosis
Secretory
vesicle
Fusion of secretory
vesicle with
plasma membrane
Secretion of
vesicle contents
(exocytosis)
Nucleus of cell
Figure 2.5
Page 27
Carrier-mediated Transport
Step 1
Molecule to be
transported
Step 2
ECF
Plasma
membrane
Conformation X
of carrier
Carrier
Concentration
molecule
gradient
Conformation Y
of carrier
ICF
Step 4
Step 3
ECF
ECF
Direction of
transport
ICF
ICF
ICF
Figure 3.14
Page 67
Active Transport
ECF
Concentration
gradient
(High)
Na+
ICF
(Low)
Dephosphorylated
conformation X
of carrier
Phosphorylated
conformation Y
of carrier
Direction of
transport
Molecule to be
transported
Step 1
Step 2
= phosphate
Figure 3.16
Page 70
Glycoprotein
Glycolipid
Extracellular fluid
Carbohydrate
chain
Lipid bilayer
Dark line
Cholesterol
molecule
Channel
Phospholipid molecule
Various
membrane
proteins
Intracellular fluid
Light space
Dark line
Appearance using
an electron microscope
Figure 3.3
Page 55
Ionic Concentrations
& Permeabilities
Ionic concentrations & Permeabilities
In Resting
in Resting Nerve
Nerve CellCell
Extracellular
(mmol/L)
Intracellular
(mmol/L)
Relati ve
Perm eability
Na+
150
15
1
K+
5
150
75
A-
0
65
0
Plasma membrane
ICF
ECF
Concentration
gradient for K+
Electrical
gradient for K+
EK+ = –90 mV
Figure 3.20
Page 76
Plasma membrane
ICF
ECF
Concentration
gradient for Na+
Electrical
gradient for Na+
ENa+ = +60 mV
Figure 3.21
Page 78
Plasma membrane
ECF
ICF
Relatively large net
diffusion of K+
outward establishes
an EK+ of –90 mV
No diffusion of A–
across membrane
Relatively small net
diffusion of Na+
inward neutralizes
some of the
potential created by
K+ alone
Resting membrane potential = –70 mV
(A– = Large intracellular anionic proteins)
Figure 3.22
Page 78
ECF
Na+–K+
pump
(Passive)
Na+ channel
K+ channel
(Passive)
(Active)
(Active)
ICF
Figure 3.23
Page 79